Debug Log errors

While it doesn’t fix the problem, if anyone else needs to stop the PHP Notice filling their debug log so they can see if anything is happening AI recommeded I do this and it seems to have done the trick:

Use a Must-Use (MU) Plugin

Must-Use plugins load before any regular plugins or theme files. This ensures your filter is active before Sliced Invoices can trigger the notice. 

1. Access your site files via FTP or File Manager.
2. Navigate to /wp-content/mu-plugins/. (If the mu-plugins folder does not exist, create it).
3. Create a new file named silence-sliced-invoices.php.
4. Paste the following code:

<?php
/**
 * Plugin Name: Silence Sliced Invoices Translation Notice
 */
add_filter( 'doing_it_wrong_trigger_error', function( $trigger, $function_name, $message ) {
    if ( $function_name === '_load_textdomain_just_in_time' && strpos( $message, 'sliced-invoices' ) !== false ) {
        return false;
    }
    return $trigger;
}, 10, 3 );

Hope this helps.