WP Simple Pay: Add Custom CSS Classes to the Payment Button

/**

 * @link https://library.wpcode.com/snippet/j57zm12g/

 */

add_filter(

	'simpay_payment_button_class',

	/**

	 * @param array $classes List of class names.

	 * @return array

	 */

	function( $classes ) {

		$classes[] = 'my-button-class-1';

		$classes[] = 'my-button-class-2';

		return $classes;

	}

);