Does it supports multiple websites?

I am having two websites on which I am configuring with one app key and secret key. And the issue get is that when adding or editing a product I cannot find the infusionsoft related fields on one website. On the second website’s admin it is working correctly. So, please let me if I can use the same keys on multiple websites? Let me know whether a single account supports multiple websites or not.

Also, getting this error in the log
[02-Aug-2023 23:40:14 UTC] PHP Fatal error: Uncaught Error: Call to a member function getRefreshToken() on null in /home/customer/www/

The error you are seeing indicates that you are trying to reuse a Refresh Token; each Refresh Token is single-use, rotating your active tokens to provide additional security. You will need to authorize each usage independently, assuming that you are trying to maintain a Refresh Token for internal use.

So, yes, you can indeed use the same Client Id and Client Secret on multiple sites and platforms, although I would recommend creating a separate Application record (and key and secret) for each so that if you have to rotate them you can do so independently rather than having joint downtime.