Add filter not working for multisite

I have this code running only at wordpress backend because I want to disable auto upload images via media library but allows visitor uploaded img to be auto watermarked.

function add_watermark( $should_apply ) {
    return false;
}
add_filter( 'easy-watermark/should-apply-watermark', 'add_watermark' );

This code run well at normal wordpress site but once I use this code at multisite, it wont works anymore. Any solution to make this code able to execute at multisite?

*remark: this code is added to Code Snippet Plugin with the setting “Only run in administration area”

• This topic was modified 4 years, 6 months ago by Sheng.
• This topic was modified 4 years, 6 months ago by Sheng.