Required Fs Method
MainWP plugin required the Filesystem Method to be set todirect to perform updates properly. If it's set to any other option, it is more than likely that some features won't work properly. To set the Filesystem to
direct, please add the following code line to the
wp-config.php file on your Child sites:
define( 'FS_METHOD', 'direct' );
Source Article:
https://kb.mainwp.com/docs/required-fs_method/