Root Cause

• Duplicate transaction attempt: The customer likely clicked the payment button multiple times, initiating multiple requests with the same token.
• Token reuse conflict: The same token is being used for multiple concurrent transactions, which the payment gateway does not allow.
• Slow network response: The initial transaction is still being processed due to delayed responses, causing subsequent requests to fail.
• Lack of idempotency handling: The integration does not handle repeated clicks or multiple submissions gracefully.

Troubleshooting and Solutions

• Advise the customer to wait for the first transaction to complete before attempting again.
• Inform the customer to avoid clicking multiple times on the payment button.
• Implement client-side controls to disable the payment button after the first click until the request completes.
• Use idempotency keys in your API calls to prevent duplicate charges and manage concurrent transaction requests effectively.
• Monitor transaction logs to ensure only one successful charge is processed for the token in use.
• If it's occurring quite often, reach out to the Chargebee support team with sample logs for further investigation.