Custom post url wrong, here’s a fix

A custom url will always be a post url because the conditional is validating against a none existing variable.

To fix it, in file acf-button-v5.php change line 828 and next lines to:

if ( 'custom' === $field['default_type'] ) {
	$url = $value['url'];
} else {
	$url  = get_permalink( $field['value']['post'] );
}