mypmpro-change-price-based-on-gateway.php

<?php
/**
 * This recipe will add a fee to the initial and recurring value when using Stripe
 * 
 * You can add this recipe to your site by creating a custom plugin
 * or using the Code Snippets plugin available for free in the WordPress repository.
 * Read this companion article for step-by-step directions on either method.
 * https://www.paidmembershipspro.com/create-a-plugin-for-pmpro-customizations/
 */
function my_pmpro_checkout_level( $level ){

	if( !empty( $_REQUEST['gateway'] ) ){

		if( $_REQUEST['gateway'] == 'stripe' ){

			$level->initial_payment = $level->initial_payment + 3;	//Updates initial payment value
			$level->billing_amount = $level->billing_amount + 3;	//Updates recurring payment value 

		}

	}
 
	return $level;

}
add_filter( "pmpro_checkout_level", "my_pmpro_checkout_level" );

This recipe is included in the blog post on "3 Methods to Adjust Membership Pricing Based on Payment Gateway" at Paid Memberships Pro here: https://www.paidmembershipspro.com/adjust-membership-pricing-by-payment-gateway/