Hello,
This looks interesting. First of all, I have to ask, have you by any chance enabled WP_DEBUG_DISPLAY in your wp-config.php? If you did, try turning it off again. When it’s on, any PHP errors from any plugin can be written out to the JSON output.
If you still see the error after turning this off:
The error indicates that one of the responses of the JSON API endpoints is malformed for some reason. Without looking at the output I cannot tell which one.
If you like, you can email me some user credentials and I can log in to your site and see what’s wrong. Administrator access is not required, simply a user with the has_wallets and related capabilities.
Another thing you can try is to disable some of the other plugins and see if it makes any difference.
Email me if you wish for me to have a closer look.
with regards