Error in WP 5.5: “register_rest_route was called incorrectly”

[PhilLehmann]

I am stumbling over this error.

It is already described over here: https://wordpress.org/support/topic/error-in-wp-5-5-register_rest_route-was-called-incorrectly/

It affects all installations of Shariff on WordPress 5.5 and newer.

[3UU]

Hi Phil, sorry you are wrong here. The WP plugin has nothing to do with the code here. So please close your report. I have added a suggestion to fix the problem at the link do you provided. But need somebody to test it. Perhaps you can help me ;-)