You can only refund WeChat Pay transactions completed within the last 365 days.
For older transactions older, you must process refunds through alternative methods, such as unreferenced refunds.
Additionally, there is a limit on the refund frequency for transactions completed within the past 60 days.
If you receive a soft decline when trying to refund a payment, try reducing the frequency of the refund request, and then try again.
In both cases, you receive a Payment refund declined webhook.