Save PayPal payer email in usermeta.

my_http_api_debug.php

<?php

/**
 * Save PayPal payer email in usermeta.
 */
function my_http_api_debug( $response, $context, $class, $r, $url ) {
    
    global $current_user;
    
    // Only continue for PayPal requests.
	if ( false === strpos( $url, 'paypal.com' ) ) {
        return;
    }
    
    // Only continue for GetExpressCheckoutDetails requests.
    // We use GetExpressCheckoutDetails to confirm the payment after returning from PayPal.
    $request = array();
    parse_str( wp_remote_retrieve_body( $r ), $request );
    if ( 'GetExpressCheckoutDetails' == $request['METHOD'] ) {
        
        // Get the payer email.
        parse_str( wp_remote_retrieve_body( $response ), $response );
        $email = $response['EMAIL'];
        
        // Save it in usermeta.
        update_user_meta( $current_user, 'pmpro_paypal_payer_email', $email );
    }
}
add_action( 'http_api_debug', 'my_http_api_debug', 10, 5 );