This would suggest that you don’t have the
Art4\JsonApiClient package installed. This should have been installed when you installed the patreon package because it’s a dependency but it seems the installation of that package failed for some reason.
A first step to try and resolve this would be to install the package manually, e.g:
composer require art4/json-api-client
If that doesn’t help, try deleting your
vendor directory then run
composer require patreon/patreon again. Do you see any errors?
As a side note, I’ll be releasing a new Patreon PHP library in the coming days that’ll make it much easier to work with the API, keep an eye out for that on this forum this week if you’re struggling with the current PHP library