Ok, this is likely a v1 installation vs v2 installation issue. Your site is an old site and therefore was set up with v1 api. This is why it is marked for v1 and the plugin is loading the v1 api class. Hence the error.
Setup wizard is set to work with v2 api and v2 clients. That is why you are experiencing this problem.
If you dont want to stay with your v1 installation and instead want to move to a v2 installation, a built-in method for this does not exist at this time. The best route is performing the below, one time operation:
1 - Deleting the existing listed app for your site at clients page:
2 - Then deleting the patreon-installation-api-version option saved in your WP’s options table in database.
Then you can re-run setup wizard.
This conundrum exists due to there not being an easy way to transition existing v1 clients to v2 clients on api side.
I am going to arrange some method to make it easier in the next release. (likely within early next week).
Until then you may stay with your v1 installation by creating a v1 client and c/ping its details, or you can perform the above steps.