send21
send21 is a non-custodial crypto payment infrastructure that enables agencies to accept blockchain payments via payment links and APIs without holding private keys. It creates payment drafts, watches the blockchain for confirmations, and delivers signed webhooks to backend systems. The platform supports Bitcoin, Ethereum, Solana, and stablecoins, with pricing locked in 161 fiat currencies. It includes an MCP server for AI agent payment initiation, Shopify integration for e-commerce clients, and support for recurring payments. Agencies use send21 to build crypto-native applications, accept international stablecoin payments, and automate payment workflows for autonomous AI agents.
send21 is an invoicing payment platform, integrating with Shopify and Muse Code. InnovaAI rates it 4.9 of 10 for agency adoption, best for Backend Engineer, AI Engineer and Account Executive roles.
Agency Audit
send21 is a non-custodial crypto payment infrastructure that lets agencies accept blockchain payments via payment links and APIs without holding private keys. It's built for teams building crypto-native applications or integrating AI agents into payment workflows. Agencies benefit most if they're already working with blockchain-based clients, building decentralized applications, or need to accept stablecoin payments from international partners. The tool handles Bitcoin, Ethereum, Solana, and stablecoins, with pricing locked in 161 fiat currencies. Adoption makes sense only if your agency's core service delivery or client base genuinely requires decentralized payment rails.
3recommended
36/mo
No paid plan published
High
Illustrative scenario. Not a guarantee. Net capacity needs a verified paid base plan, and none is published for this service, so it is not modeled. Hours saved come from the service estimate; implementation, taxes, and unprovided usage charges are excluded.
- Backend Engineer handling crypto payment integration and testing
- AI Engineer handling blockchain payment reconciliation
- Account Executive handling international client payment coordination
- Your client base is primarily traditional businesses (e-commerce, SaaS, agencies) that pay via credit card, ACH, or invoice, and you have no active crypto or blockchain projects in your pipeline.
- Your team has no in-house blockchain or smart contract expertise, and onboarding send21 would require hiring or extensive training that doesn't align with your service offerings.
- Your agency operates in a jurisdiction with unclear or restrictive crypto payment regulations, and compliance risk outweighs the operational benefit of accepting blockchain payments.
Internal Adoption Path
No paid plan published
36 hr/mo
3 seats × 12 hr each
$2,700/mo
modeled at $75/hr labor rate
No paid plan published
Illustrative scenario. Not a guarantee. No verified paid base plan is published for this service, so subscription cost and net capacity are not modeled. Implementation, taxes, and unprovided usage charges are excluded.
Platform Features
Core capabilities of send21
Draft-only API keys for AI agents
Scoped API keys allow AI agents and backend systems to create payment drafts without access to private keys or spending authority. Developers can test live-network payments safely by creating small drafts to their own address, eliminating the need for custodial intermediaries and reducing security risk for teams building autonomous payment workflows.
Multi-chain payment links and QR codes
Generate hosted payment pages with QR codes that accept Bitcoin, Ethereum, Solana, and stablecoins across multiple networks. Project managers and account executives can share a single link with clients instead of managing separate payment instructions per blockchain, reducing payment coordination overhead.
Signed webhook confirmations
send21 watches the blockchain and delivers cryptographically signed webhooks when payments confirm. Backend teams eliminate manual chain-polling and reconciliation work, automating payment verification for invoicing, fulfillment, and accounting workflows.
Recurring payment scheduling
Support for daily, weekly, and monthly recurring payments lets agencies set up subscription-like billing for retainer clients on blockchain rails. Operations teams avoid manual payment reminders and reduce churn from missed one-off payments.
161 fiat currency pricing with locked rates
Price payments in any fiat currency with exchange rates locked at draft creation time. Account executives can quote international clients in their local currency without exposing the agency to crypto volatility between quote and settlement.
MCP server for Claude and other AI frameworks
send21 provides a Model Context Protocol server that integrates directly with Claude and compatible AI frameworks. AI engineers can build agents that initiate payments as part of autonomous workflows without writing custom API wrappers.
What Makes send21 Different
Unique advantages vs similar tools in this niche
Non-custodial architecture with scoped API keys for AI agents
vs Custodial payment gateways like Coinbase Commercesend21 never holds funds or private keys, and AI agents can create drafts but cannot spend, reducing risk.
Usage-based pricing with no subscription or minimum fees
vs Subscription-based crypto payment processorsFees start at 0.49% and decrease to 0.01% for large payments, with a maximum of $100 per transaction.
Value Equation
Outcome-likelihood-time-effort assessment for send21
Limited agency channel
send21 scored below the agency-resellability threshold (agency_fit_score < 50). The Value Equation projects agency-side outcomes, which don't apply to tools without a clear resell pathway.
Contact send21Pricing
send21 platform cost to your agency
Pay as you go
- No monthly subscription required
- Pay only for what you use — see per-unit rates below
- Cancel anytime, no contract lock-in
How usage-based pricing works
send21 charges per consumption unit (per payment $100,000+ (0.01%)). Below are the component rates the vendor publishes. Each row is a separate charge: your total cost combines them based on your configuration and volume. Component rates range from $0.0001 per payment $100,000+ (0.01%).
Final agency cost = (sum of selected component rates) × client usage volume. Confirm a usage estimate with each client before quoting.
Component Rates
Cost per unit: total depends on your configuration and volume
Add-ons
Optional extras priced on top of any main plan
No verified white-label program for send21: client-facing delivery runs under the platform's native branding.
Market Intelligence
Offer + scale economics for send21
Limited agency channel
send21 scored below the agency-resellability threshold (agency_fit_score < 50). It's a useful tool but not designed for white-labeled or retainer-based reselling, so we don't publish productized offer economics for it.
Contact send21Investment Decision Framework
Strategic vetting analysis for send21
Situational Fit
Fit depends on your client mix
Buy If
4Your development team builds crypto-native applications or decentralized finance integrations for clients 5+ hours per week, and currently relies on manual payment coordination or third-party custodial services that slow deployment.
Your agency accepts international payments from crypto-native clients and needs to reduce settlement time and currency conversion friction compared to traditional banking rails.
Your AI engineering team is building autonomous agents that need to initiate payments without human key custody, and you're currently blocked by the lack of a non-custodial payment API.
Your project managers spend 3+ hours per week managing payment disputes or reconciliation across multiple blockchain networks, and send21's webhook confirmation system would replace that manual tracking.
Skip If
4Your agency operates in a jurisdiction with unclear or restrictive crypto payment regulations, and compliance risk outweighs the operational benefit of accepting blockchain payments.
You need a payment processor that handles chargebacks, disputes, and customer support for non-technical users, send21 is designed for developers and assumes wallet literacy on the payer side.
Your client base is primarily traditional businesses (e-commerce, SaaS, agencies) that pay via credit card, ACH, or invoice, and you have no active crypto or blockchain projects in your pipeline.
Your team has no in-house blockchain or smart contract expertise, and onboarding send21 would require hiring or extensive training that doesn't align with your service offerings.
Bottom Line
send21 is a non-custodial crypto payment infrastructure that lets agencies accept blockchain payments via payment links and APIs without holding private keys. It's built for teams building crypto-native applications or integrating AI agents into payment workflows. Agencies benefit most if they're already working with blockchain-based clients, building decentralized applications, or need to accept stablecoin payments from international partners. The tool handles Bitcoin, Ethereum, Solana, and stablecoins, with pricing locked in 161 fiat currencies. Adoption makes sense only if your agency's core service delivery or client base genuinely requires decentralized payment rails.
Reality Check
send21 solves a narrow problem: crypto payment infrastructure for agencies already operating in blockchain space. If your agency builds traditional web or mobile apps, or your clients pay via ACH and credit cards, this tool adds no operational value. The learning curve for team members unfamiliar with blockchain concepts and wallet signing workflows is real.
Moderate effort: standard configuration with some customization needed
Academy for send21
Work through it in order: the course for this service first, then the modules behind it.
Course for this service
send21 Agency Implementation, Crypto Payment Workflows for AI Agents
Learn how to build crypto payment infrastructure for your clients using send21's non-custodial API and draft-only keys. This course covers accepting stablecoin payments across Bitcoin, Ethereum, and Solana, automating payment workflows with AI agents via MCP servers, and delivering recurring billing without holding client funds.
Open the courseNo Academy modules are published for this service yet. Browse the full Academy
Why this category matters
The commercial case before the tooling.
Core concepts
The mental model you need to price and scope the work.
- Reminder Cadence LadderConcept
Reminder Cadence Ladder is a framework for treating payment collection as a scheduled sequence rather than an act of willpower. Each rung of the ladder fires at a fixed interval after invoice delivery: a pre-due nudge, a due-date confirmation, a short grace window, then a firmer escalation with a named account contact. The point is that most agency DSO is not caused by clients refusing to pay; it is caused by invoices sitting unseen in an inbox while the account manager waits to avoid seeming pushy. Automating the ladder removes that social friction and makes the follow-up the system's job, not a person's. The category description frames the leverage exactly here: reducing days sales outstanding through automated reminders and payment gateways. A concrete illustration sits in the tooling itself, where platforms such as Invoice Ninja and Xero pair recurring billing with scheduled dunning, and Agicap extends the same logic to 13-week cash forecasting so an agency can see the ladder's effect on liquidity before month end.
- Collection Friction MapConcept
Collection Friction Map treats days sales outstanding as a sum of small frictions rather than one big delay. Each handoff in the invoice-to-cash path (time capture, approval, invoice send, payment method, reconciliation) adds hours or days, and agencies usually fix the loudest one while ignoring the compounding ones. Map every step, count the elapsed days at each, then attack the widest gap first. A studio billing through Harvest may find that time-to-invoice is fast but clients still pay late because the only option is a bank transfer; adding a card or direct debit gateway such as GoCardless at the invoice level often moves more cash than another reminder email. The framework matters because retainer agencies run on predictable inflows, and a five-day DSO improvement on $80k monthly billings frees roughly $13k of working capital. Audit the path quarterly, since client payment behavior shifts with their own budget cycles.
- Billing Signal LatencyConcept
Billing Signal Latency is the elapsed time between work performed and the moment a client can actually pay for it. Every handoff in that chain (timer to timesheet, timesheet to approver, approval to invoice, invoice to gateway) adds delay that compounds into days sales outstanding. Agencies feel it as a cash flow problem, but the root cause is usually a data problem: hours logged late, expenses missing receipts, or invoices batched to month-end because nobody owns the conversion step. Harvest's time-to-invoice conversion is the canonical example of compressing this chain, while Xero's bank reconciliation and cash forecasting show what becomes possible once the signal arrives clean. The framework matters because reminder automation cannot rescue an invoice that was never sent; shortening latency upstream of collection is cheaper than chasing payment downstream. Measure it per client, not per agency, since retainer accounts and project accounts fail at different points.
Decision and risk
How to judge the fit, and the ways it goes wrong.
- Invoicing Rule: Measure DSO Before Adding Another Payment GatewayEvaluation Rule
Instrument days sales outstanding and reminder automation first, and only then decide whether a new invoicing platform earns a place in the stack.
- When Billing Runs on One Platform, Map the Fallback Before the Next Retainer CycleEvaluation Rule
Document a tested fallback path for invoice generation and payment collection before renewing any single-platform billing dependency.
- Invoicing & Payments Decision: Automated DSO Compression vs Manual Billing ToleranceDecision Framework
IF billable work is spread across more than three concurrent client retainers and invoices routinely clear past 30 days, THEN build an automated time-to-invoice-to-reminder chain with a payment gateway attached, because the cash drag compounds faster than the tooling cost. IF the agency runs fewer than five active clients on fixed-fee retainers with a bookkeeper already reconciling monthly, THEN keep manual invoicing and spend the budget on delivery instead.
- Why Invoicing & Payments Stalls When Billing Data Lives in Three SystemsFailure Pattern
- The Silent DSO Trap: Why Invoicing & Payments Leaks Cash After the Invoice SendsFailure Pattern
Delivery system
Blueprints and procedures for running it as a service.
- DSO Reduction and Billing Automation Offer (10-14 days)Implementation Blueprint
A fixed-scope engagement that rebuilds an agency client's time-to-cash path: tracked hours and expenses convert into invoices on a schedule, reminders fire without a human, and a payment gateway closes the loop. Target outcome is a measurable drop in days sales outstanding within two billing cycles.
- Billing Data Handoff to Finance (Handoff)Operating Procedure
- Deposit-to-Invoice Reconciliation (Onboarding)Operating Procedure
- Days Sales Outstanding Recovery Sequence (Retention)Operating Procedure
13 modules selected for send21
Frequently Asked Questions
Answers about pricing, setup
send21 is a non-custodial crypto payment infrastructure that lets agencies and their clients accept blockchain payments without holding private keys. It creates payment drafts via API or payment links, watches the blockchain for confirmations, and delivers signed webhooks to backend systems. The tool supports Bitcoin, Ethereum, Solana, and stablecoins, with pricing locked in 161 fiat currencies. It includes an MCP server for AI agent payment initiation and integrates with Shopify for e-commerce clients.
send21 has a free plan; its paid prices are not published.
Backend and AI engineers benefit most, as they can build autonomous payment workflows and integrate crypto payments into applications without custodial risk. Account executives and project managers gain value if they manage crypto-native clients or international retainers, since send21 eliminates manual payment coordination across blockchains. Founders of agencies building decentralized applications or accepting stablecoin payments from global partners see the fastest ROI.
For backend teams building crypto-native applications, send21 saves 3-5 hours per week by eliminating manual payment reconciliation and webhook polling. For account executives managing international crypto clients, it saves 2-3 hours per week on payment coordination and currency conversion overhead. For teams not actively building blockchain products or accepting crypto payments, the tool saves zero hours and adds no operational value.
Yes. Backend developers need familiarity with blockchain concepts, wallet signing, and API integration. Account executives and project managers need to understand that payers must sign transactions in their own wallets, which is different from traditional payment flows. If your team has no crypto experience, onboarding will require training or hiring. send21 is designed for developers and assumes wallet literacy on both the agency and client side.
send21 does not handle chargebacks or disputes because blockchain payments are irreversible by design. If a client needs a refund, you must initiate a new payment back to their wallet. This is fundamentally different from credit card processing. Your agency must have clear refund policies and client communication workflows in place before accepting blockchain payments.
send21 delivers signed webhooks when payments confirm, which your backend can use to trigger accounting entries or invoice updates. Direct integrations with accounting platforms are not listed. Your development team will need to build a webhook receiver that connects send21 confirmations to your accounting system, or use Zapier-style automation if available.
send21 does not hold private keys or custody of funds, so there is no data migration risk. Payment history and draft records remain accessible via API until you delete them. Since payments are recorded on the blockchain itself, you retain a permanent, immutable record of all transactions regardless of send21 account status.