Adds extra column in Affiliates > Total, Export file for custom registration field with name extra_field

functions.php

add_filter( 'affiliates_totals_export_file_headings', 'example_affiliates_totals_export_file_headings' );
function example_affiliates_totals_export_file_headings( $headings ) {
	$headings[] = 'Data';
	return $headings;
}

add_filter( 'affiliates_totals_export_file_line', 'example_affiliates_totals_export_file_line', 10, 4 );
function example_affiliates_totals_export_file_line( $line, $affiliate_id, $user_id, $result ) {
	
	$extra_field = get_user_meta( $user_id, 'extra_field', true );
	if ( $extra_field ) {
		$line['suffix'] = $extra_field;
	}
	return $line;
}