URI mismatch error (still)

I know this topic appeared earlier, but I still have got those issues when my Patrons try to unlock a post through a button.
I’ve checked and redirect URI is exactly the same in both places (with https:// and / at the end) and — as far as I know — my Wordpress is using only https (it uses Really Simple SSL plugin that should take care of that).

For what is worth, I recenlty changed the hosting provider and installed SSL certificate that wasn’t there before.

Where should I look for solution? I even created a new API client on Patreon’s site to check if something is wrong there. What other options do I have?

Can you reproduce this by using a test patron account you create? First its needed to confirm whether this is a common issue or issue specific to certain patrons and their browser/os/device/isp.

Yes, I’ve just confirmed that. I am unable to login to this Wordpress site using Log In With Patreon button. The same „Mismatching redirect URI.” error occurs.

This is prettty odd. Can you double check details for your client id in the plugin settings and the one saved at Patreon? You could be using another client than you intented to use for that site.