Very basic custom RESTful API to check the membership level of a Paid Memberships Pro User

my_init_pmpro_mini_api.php

<?php
/**
 * Call to http://yoursite.com/[email protected]&secret=SOMESECRETHERE to check the membership level of a user.
 */
function my_init_pmpro_mini_api() {
	if ( function_exists( 'pmpro_getMembershipLevelForUser' ) && 
		! empty( $_REQUEST[ 'verify' ] ) && 
		! empty( $_REQUEST[ 'secret' ] ) )
	{
		if ( $_REQUEST[ 'secret' ] != 'SOMESECRETHERE' ) {
			wp_die( 'Invalid secret.' );
		}
			
		$user = get_user_by( 'email', str_replace( ' ', '+', ( $_REQUEST['verify'] ) ) ) ;
		if ( empty( $user ) ) {
			wp_die( 'User not found.' );
		}
			
		$membership_level = pmpro_getMembershipLevelForUser( $user->ID );
		if ( empty( $membership_level ) ) {
			die( '0' );
		}
			
		//If User and membership level found, output json encoded membership level info.
		echo json_encode( $membership_level );
	
		exit;
	}
}
add_action( 'init', 'my_init_pmpro_mini_api' );

This recipe is included in the blog post on "Interacting with Paid Memberships Pro Through APIs" at Paid Memberships Pro here: https://www.paidmembershipspro.com/interacting-with-paid-memberships-pro-through-apis/