agmail Inbox 4-Hour Renewal (MPP)

Use this endpoint specifically when you need to extend an existing agmail inbox by exactly 4 hours via the Micropayment Protocol (MPP) and you already have the inbox_id and secret. Prefer this over other agmail sibling endpoints when your agent is mid-task and the inbox is about to expire and you want to pay programmatically in USDC stablecoins without manual intervention. If you need a different duration or are creating a new inbox rather than renewing, use the appropriate sibling endpoint instead.

• Invalid or mismatched inbox_id and secret — returns an authentication or not-found error
• Inbox does not exist or has already permanently expired — returns a 404 or invalid-state error
• Payment settlement failure or insufficient stablecoin balance — renewal remains queued but may not apply
• Malformed inbox_id (not matching pattern ^ib_[0-9a-f]{12}$) — returns a validation error
• Network or service timeout — payment may have been processed but status unknown, requiring a GET poll