wpmem_product_restricted_msg

add_filter( 'wpmem_product_restricted_msg', 'my_product_restricted_msg', 10, 2 );
function my_product_restricted_msg( $msg, $post_products ) {
    
    $msg = "This is post is restricted.";

    return $msg;
}

/**
 * This example checks the products array in the filter
 * to see if there is more than one product. If it is
 * just one, it creates a simple message string of:
 * "Sorry, you must have a {name of product}" message by
 * getting the product title from the membership products
 * object in the main $wpmem object class.
 *
 * But if there are multiple products assigned, it loops
 * through and builds a string so that the product names
 * are separated by commas, with the last one adding
 * an ", or". This is a good example of how to work with
 * arrays in PHP.
 *
 * Follow the comments to get a handle on what the snippet
 * is doing at each logical step.
 */
add_filter( 'wpmem_product_restricted_msg', 'my_custom_product_restricted_msg', 10, 2 );
function my_custom_product_restricted_msg( $msg, $post_products ) {
    
    // You will need the global $wpmem object.
    global $wpmem;
    
    // Assemble a string with the product titles.
    // If $post_products array is more than one product:
    if ( count( $post_products ) > 1 ) {
        
        // Start with an empty container:
        $products = '';
        
        // Loop through the products to get their titles:
        foreach ( $post_products as $key => $post_product ) {
            
            // If this is the end of the product array, add ", or".
            // Note .= adds to the whatever is in the existing string $products
            end( $post_products );
            if ( $key === key( $post_products ) ) {
                $products .= "or " . $wpmem->membership->products[ $post_product ]['title'];
            } else {    
                // Otherwise, if this is not the end, add a comma/space:
                $products .= $wpmem->membership->products[ $post_product ]['title'] . ", ";
            }
        }

    } else {
        // OR... if $post_products array is just one product:
        $products = $wpmem->membership->products[ $post_products[0] ]['title'];
    }

    // Put the assembled $products string into your custom message:
    $msg = "Sorry, you must have a " . $products . " membership to access this content.";
    
    // Return the custom message.
    return $msg;
}