How to choose a blockchain payment API: a technical buyer's checklist

A blockchain payment API lets your product move money over stablecoin networks through ordinary REST calls. You create quotes, payins, and payouts. The provider handles wallets, chains, conversion, and the bank rails at each end. Picking one comes down to seven checks, and most of them can be done with the docs and a sandbox key before anyone books a sales call.

This checklist is for the engineering lead or PM who will live with the integration for years. The commercial questions (pre-funding, settlement speed, contract terms) are covered in how to choose a stablecoin API. This page is about the API surface itself: what you'll actually type, test, and debug.

Each section says why the criterion matters, what a good answer looks like, and how BlindPay handles it. The summary table is at the end.

1. Which languages do the SDKs cover?

SDKs decide how much glue code you write and how fast you notice a breaking change. A good answer is an official SDK in your backend language, versioned, and built from the same spec the API is validated against, so a field can't exist in one and not the other. Typed amounts and typed webhook payloads are a bonus that pays for itself the first time someone mixes up cents and dollars.

BlindPay: five official SDKs (Node.js/TypeScript, Python, Go, PHP, and Swift) wrap the same REST API. For any other language, generate a typed client from the OpenAPI spec. There is also a CLI and an MCP server for AI coding agents. How one spec keeps the SDKs in sync is covered in stablecoin API SDKs.

2. Is the REST API documented by a real OpenAPI spec?

A downloadable, machine-readable spec lets you generate types, mock the API in tests, and diff versions in CI. Hand-written reference pages drift. Look for five things:

• An OpenAPI 3.x spec you can download without logging in
• Idempotency on every mutating request, so a retry after a timeout can't create a second payout
• Signed webhooks with a stable event ID you can deduplicate on
• Amounts as integers in minor units, never floats
• A sandbox that behaves like production, including failure states

BlindPay: the OpenAPI 3.1 spec downloads from https://api.blindpay.com/doc. Any POST, PUT, PATCH, or DELETE accepts an Idempotency-Key header of up to 255 characters, and a retry only replays when the body is byte-identical (idempotency). Webhooks are signed with svix-id, svix-timestamp, and svix-signature headers, and svix-id stays the same across redeliveries (webhook verification). Amounts are minor units: 10000 is $100.00. The practical side of both is in idempotency keys and webhooks and reconciliation.

3. Does the API hide the blockchain, or expose it?

This is the criterion most checklists skip, and it splits buyers into two groups.

A payroll, remittance, or B2B payments product wants bank-shaped building blocks: an account number in, a bank payout out, the chain invisible. A wallet, exchange, or treasury product wants to pick the chain and token, hold its own keys, and sign authorizations. An API built for only one group forces the other into workarounds. The good answer is both, on one engine, with no second contract or second set of keys.

BlindPay: the docs come in two flavors of the same API. Both run on the same authentication, instances, and webhooks, and switching between them changes nothing about your account or key (introduction).

Advanced exposes the on-chain mechanics: ERC-20 approve on EVM chains, a signed XDR on Stellar, token delegation on Solana. Abstracted never asks you to sign anything.

4. Which networks does it settle on, and who picks the network?

Network choice affects fees, confirmation time, which stablecoins are available (USDT dominates on Tron, for example), and which wallets your customers already hold. For the end user, though, it's mostly noise. A good API covers the major networks, gives you a testnet for each, and lets you keep the network out of the user's way in bank-to-bank flows.

BlindPay:

Tron has no testnet. Development instances use USDB, a test token that simulates transactions without real funds, on every testnet above (supported chains). USDC can move cross-chain between managed wallets through Circle's CCTP v2. What actually happens on each network between "sent" and "confirmed" is in what happens on-chain in a stablecoin payment.

5. Is compliance built into the API or bolted on?

If KYC, KYB, and sanctions screening live with a separate vendor, you own the plumbing between them: status syncing, document uploads, re-verification, and the audit trail that links an identity to a payment. Built in means every payment object belongs to a verified customer and can't execute for an unverified one. Look for verification statuses in the API, a way to answer requests for information programmatically, and documented review states on payments.

BlindPay: every payment flows through a customer that has completed KYC. You collect the data, BlindPay verifies it. Standard KYC takes about 60 seconds; KYB takes 3 hours to 1 business day because a person reviews it (cut-off times and SLAs). Payments that need review sit in an on_hold status you can see and react to. More on the automation side in how to automate KYC and KYB.

6. Which local payout rails are live in production?

The stablecoin leg is the easy part. The rail at the end decides whether the recipient gets paid in minutes or in a week. A good answer names each rail, publishes a settlement window and cut-off for each, and documents the required fields per rail. "Coming soon" doesn't count.

BlindPay: Pix and TED in Brazil, SPEI in Mexico, Transfers in Argentina, ACH COP in Colombia, ACH, wire, and RTP in the US, SEPA in Europe, and SWIFT (POBO/COBO) to 100+ countries with UETR tracking and MT103 confirmations. Pix, SPEI, Transfers, and RTP are instant; wire, SEPA, and ACH COP take about 1 business day; ACH about 2; SWIFT about 5 (bank accounts). The per-country breakdown is in stablecoin payout settlement times.

7. Can you see the price before you sign, and is there a volume floor?

You'll model unit economics per corridor, so you need numbers you can reproduce. Watch for three things: a minimum monthly volume commitment, a pre-funding requirement (capital parked in the provider's accounts is a cost even when it isn't a line item), and a blended rate that hides the FX spread inside one number.

BlindPay: plans are listed on the pricing page. There is no setup fee and no monthly minimum, and development instances are free. Transaction fees vary by rail and corridor, so every payin, payout, and transfer quote itemizes the fee before you execute, and the fee is locked for the life of the quote (billing). Payouts don't require pre-funding. For how to read a quote line by line, see stablecoin API pricing.

What should you ask on the technical evaluation call?

Three questions, and each one exposes a different weak spot.

1. "Show me a payout that failed at the receiving bank." Which status did it land in, which webhook fired, and where did the money go? At BlindPay, a payout the bank rejects or returns ends refunded and the stablecoins go back to the wallet that funded it. A payout that ends failed, for example after a rejected compliance check, does not refund on its own and needs a support follow-up. A vendor that can't draw that line clearly hasn't thought about it.
2. "Can I have the OpenAPI spec and a sandbox key today?" If either requires a contract, your evaluation just got two weeks longer.
3. "Which of your listed rails and networks are live in production for a company like mine, and which are beta?" Marketing pages list everything. Production access is often narrower, and it can depend on where your company and your customers are based.

The checklist at a glance

What to do next

Run the checklist against a live sandbox, not a slide deck. Create a free BlindPay development instance, download the spec, and push one payin and one payout through end to end with the payout quickstart. Then force a failure (a payout quote for $777.00 returns refunded in development) and watch what your webhook handler does with it. That hour tells you more than any vendor call.

Once you pick a provider, rails-first vs chain-first explains BlindPay's Abstracted and Advanced API flavors and what each changes in your code.

This article is for general information only and is not legal, tax, or financial advice.