MemberPress does not have anti double click on the `#payment-form` submit button, which can result in duplicate payments/subscriptions with the Pronamic Pay plugin. This can be fixed by adding this gist to the `functions.php` file of the WordPress theme.

memberpress-prevent-duplicate-payment.php

<?php

/**
 * Prevent double click on MemberPress payment form (#payment-form).
 *
 * @return void
 */
add_action( 'wp_footer', 'memberpress_prevent_duplicate_payment' );

function memberpress_prevent_duplicate_payment() {
	?>

	<script type="text/javascript">
	(function($) {
		$(document).ready( function() {
			$('body').on( 'click', '#payment-form .mepr-submit', function( e ) {
				e.preventDefault();

				this.disabled = true;

				jQuery( this ).parents('form').submit();
			});
		});
	})( jQuery );
	</script>

	<?php
}