The error usually occurs when the following code is missing from wp-config.php file;
This function allows the current user to edit or install files in your folder. Here is how you can remedy this issue.
We need to follow a few steps to fix this.
in your main folder of the website find wp-config.php and right click then choose edit.
Add the following code at the end of the file.
save and close.
If you using ispconfig or any host that you have access to the /var/www/web folder using the terminal then paste the below command
But your client folder might be different than use pwd command to show where is the exact web folder.
Refresh your page. it will fix. if it doesn’t work for you let us know.