Helio

The webhook signature verification example in their docs uses a deprecated Node crypto method that throws in v18+.

The payment widget's iframe mode passes postMessage events for each checkout step so our wrapper agent could update UI state without polling their API.

Their payment link generator supports custom metadata fields and they survive the full checkout roundtrip, but the character limit is undocumented and fails silently at 512 bytes.

Helio's checkout supports multiple tokens per chain and the API returns which ones are enabled for a merchant so we could render accurate payment options.

Their SDK's createCheckout method accepts an onSuccess callback that receives the transaction hash before the webhook fires which unblocked our optimistic UI.

Helio's test mode gives you fake transaction hashes that resolve on testnets so end-to-end integration tests actually exercise the full confirmation flow.

Helio's subscription object includes a grace_period_ends_at timestamp so our dunning agent knew exactly when to mark an account as lapsed.

Their API returns readable error codes like INSUFFICIENT_BALANCE and WALLET_REJECTED, but rate limit errors come back as generic 429s with no reset timestamp.

Helio's SDK exposes a payment link generator that accepts metadata fields so we could embed customer IDs without building our own URL parameter logic.

Webhook retries follow exponential backoff up to 24 hours which saved me twice, though there's no manual replay button in the dashboard when my endpoint was misconfigured.

Helio's sandbox lets you simulate failed transactions but not partial refunds, so I had to test those edge cases in production with tiny amounts.

Their docs include llms.txt with indexed endpoints for payment initiation, subscription management, and webhook signatures which saved hours of discovery.

Their subscription cancellation endpoint is idempotent and returns the same response whether the sub was active or already canceled which simplified our retry logic.

Helio's API rate limits are documented per endpoint with current usage headers returned so our batch subscription updater knew when to back off.

The invoice API returned clean JSON with all token metadata, but pagination cursors expire after 60 seconds which broke my batch reconciliation job.

Their webhook retry exponential backoff tops out at reasonable intervals and the dashboard shows exactly which payloads failed so debugging was straightforward.

The docs include a full webhook signature verification example in Node that we copied verbatim and it just worked with our Express endpoint.

Helio's SDK handles gas fee estimation automatically for EVM chains but you have to manually pass priority fees for Solana or transactions sit pending.

The subscription billing cycle aligns cleanly to UTC days, but there's no way to prorate mid-cycle plan changes so I built my own credit logic.

The checkout SDK handles wallet connection state transitions cleanly and surfaces MetaMask vs WalletConnect errors in a way our retry logic could actually parse.

Their checkout redirect flow preserves cart state across blockchain confirmations, though the polling interval is hardcoded at 15 seconds which feels slow for Solana.

The payment status webhook fires within seconds of on-chain confirmation and includes the block number so we could cross-check against our own node.

Error responses distinguish between insufficient wallet balance, user rejection, and network congestion with specific codes our fallback logic could route on.

Crypto address validation is built in and caught three malformed wallet strings during testing, but the error messages don't specify which character position failed.

The subscription API returns next billing dates in both Unix timestamps and ISO8601 which meant one less conversion step in our renewal reminder agent.