Plugin Support
qtwrk
(@qtwrk)
Hi,
could you please screenshot me your dropdown menu , like my screenshot

Best regards,
If you hook me up with an email, I can give you admin access to the website (multiple sites have the same problem, so knock yourself out on this staging env)
Plugin Support
qtwrk
(@qtwrk)
please create a ticket by mail to support at litespeedtech.com with reference link to this topic
we will investigate furhter.
The Support solved my issue. Wanted to share the solution here for everyone.
Problem: UCSS uses a callback path for the creation of the ucss files (/wp-json/litespeed/v1/) .
Unfortunately, this path (/wp-json) is not accessible while using the wordpress permalink structure “plain”.
For the plain permalink structure, the correct link to the wp-json endpoint is /?rest_route=.
Solution 1: Change the permalink structure in the wordpress settings
Solution 2: Change the callback uri for the ucss creation to /?rest_route=/litespeed/v1/ (not sure if that is possible without changing the plugin code)