Known limitations

• Direct x402 and MPP facilitator settlement is controlled on Stacks testnet.
• Mainnet facilitator settlement and sponsorship are disabled.
• Partner OAuth/MCP enrollment remains invite-only.
• MPP uses USDCx; the hosted x402 resource currently exercises the STX profile.
• Browser signing requires a compatible Stacks wallet such as Leather.
• Headless custody requires an application-owned secret manager, KMS, HSM or isolated signer.
• Indexer availability can delay observations even when chain state is correct.
• A transaction broadcast or pending status is not confirmed settlement.
• The API schema is a versioned snapshot and displays its last verification date; runtime challenges remain authoritative for price, recipient and payment requirements.

These limitations are deliberate rollout and security boundaries, not instructions to bypass checks. Consult deployments and payment safety before an integration moves beyond read-only evaluation.