Generate custom order codes / order numbers that increment for Paid Memberships Pro Orders [Custom order sequence]

custom-pmpro-order-codes.php

<?php
/**
 * Custom order codes for Paid Memberships Pro Orders.
 * This code will take the order ID and create an order code from that such as "INV1", "INV2", "INV3" and increment with each order added.
 * A fallback is in place that if "INV1" already exists for some order, it will just generate a random code to be safe.
 * Add this code to your PMPro Customizations Plugin - https://www.paidmembershipspro.com/create-a-plugin-for-pmpro-customizations/
 * www.paidmembershipspro.com
 */

function pmpro_custom_order_codes( $code ) {
	
	global $wpdb;

	$last_id= $wpdb->get_var( "SELECT `id` FROM $wpdb->pmpro_membership_orders ORDER BY `id` DESC LIMIT 1" );

	$current_id = (int) $last_id + 1;

	$prefix = apply_filters( "pmpro_custom_order_prefix", "INV" ); // You can change "INV" to something else or filter this from another plugin or custom code.

	$code =  $prefix . $current_id; //Code cannot just be an integer and _must_contain_a_string_.

	// We need to add a check to see if the order code is not taken, otherwise it will be an infinite loop.
	$check = $wpdb->get_var( "SELECT `id` FROM $wpdb->pmpro_membership_orders WHERE code = '$code' LIMIT 1" );

	// If the code already exists or is only a number, just generate a random order code with 10 digits.
	if ( $check || is_numeric( $code ) ) {
		$code = wp_generate_password( 10, false, false );

	}

	return $code;

}
add_filter( 'pmpro_random_code', 'pmpro_custom_order_codes', 10, 1 );

This recipe is included in the blog post on "How to Use Sequential Order Numbers for Member Invoices" at Paid Memberships Pro here: https://www.paidmembershipspro.com/how-to-use-sequential-order-numbers-for-member-invoices/