Tryin to Filter Posts by Date

Hello,

I’m trying to use the code here (https://www.wpallimport.com/documentation/developers/code-snippets/#filter-posts-by-date) to update only some posts with certains dates of a recurring import.

The result is that all posts are skipped, even those that should be updated

Here is the code i’m using

function filter_by_date( $continue_import, $data, $import_id ) {

$import_id = ( isset( $_GET['id'] ) ? $_GET['id'] : ( isset( $_GET['import_id'] ) ? $_GET['import_id'] : 'new' ) );

    if ( in_array( $import_id, [12, 23] ) ) {

         // Change 'column_4' to your file's date field.
        $date_in_file = strtotime( $data['last_mod'] );

        // Change '2018-10-10' to your real target date.
        $date = "2021-04-28 00:00:00";

        // Convert specified date to Unix timestamp.
        $target_date = strtotime($date);

        // Compare file date with target date.
        if ( $date_in_file >= $target_date ) {

            // Create or update record if file date >= target date.
            return true;

        } else {

            // Do not create or update the record otherwise.
            return false;

        }
    }

    // Take no action for other import IDs.
    return $continue_import;

}

// Apply the code to posts set to be created.
add_filter('wp_all_import_is_post_to_create', 'filter_by_date', 10, 3);

// Apply the code to posts set to be updated.
add_filter('wp_all_import_is_post_to_update', 'filter_by_date', 10, 3);

And this is the format of {last_mod[1]}: 2021-04-28 12:15:30

I also enabled debugging and it get this warning:

PHP Warning: Illegal string offset ‘last_modified’

So, is there any way to make it work?