Use this code snippet to add a shortcode that will replace [date] and [user_id] shortcodes with the current date and the current user ID before sending the API action.

add_action( 'frm_trigger_api_action', 'add_shortcodes_to_api_request', 1 );
function add_shortcodes_to_api_request() {
	add_filter(
		'frm_content',
		function( $value ) {
			$value = str_replace( '[date]', FrmProAppHelper::get_date( 'Y-m-d' ), $value );
			$value = str_replace( '[user_id]', get_current_user_id(), $value );
			return $value;
		}
	);
}