Masteriyo is a contemporary LMS that relies on react for quick responses. For each course and course page on Masteriyo, there is a “Buy Now” text link. You can modify the wording in the excerpt below to whatever you choose.

add_filter( 'masteriyo_course_add_to_cart_text', function( $text ) {
	return __( 'Buy Right Now', 'textdomain' );
});

add_filter( 'masteriyo_single_course_add_to_cart_text', function( $text ) {
	return __( 'Buy Right Now', 'textdomain' );
});