<?php include_once 'include/init.php'; //include particular file for entity you need (Client, Invoice, Category...) include_once LIB_PATH . "/FreshBooks/Invoice.php"; $clientId = 4; //new Invoice object $invoice = new FreshBooks_Invoice(); //populate data $invoice->clientId = $clientId; $invoice->date = '2011-05-06'; //mysql format //all other required properties should be populated //lines (items) is array of asoc. arrays $invoice->lines = array(array('name' => 'xyz', 'unitCost' => 99.98999999999999), array('name' => 'yyy', 'unitCost' => 199.99)); //try to create new invoice with provided data on FB server if (!$invoice->create()) { //read error echo $invoice->lastError; } else { //investigate populated data print_r($invoice); }