Serial Timeouts and Retry Guidance

Recommended values:

• Frame payload read timeout: 5 s
• Initial command response timeout: 30 s
• /check polling interval: 1000-2000 ms

Retry guidance:

• If client did not receive response frame, operation state is unknown.
• If CRC check fails on a received frame, treat response as not received.
• Recover payment state via /check using the same pay_id and trans.
• Do not blindly resend /cancel, /refund, and /final_confirm on timeout.
• For /showqrcode, prefer /check-based recovery before retrying.