Using AddTransaction API to issue a credit for invoice

[TBroMEM]

In the application, you can open a paid invoice and issue a Refund and set the Refund Type as 'Add to Client's Credit Balance'. 

What is the correct API request for this? Would the following work (sample is using localAPI from a hook? I don't see a description available when issuing from invoice refund, so not sure it applies. Also, is amountout correct?

		//Add create credit from refund transaction
		$command = 'AddTransaction';
		$values = array(
		'invoiceid' => $invoiceid, // this would be passed in as declared var
		'transid' => 'Test',
		'userid' => $clientid, // this would be passed in as declared var
		'description' => 'Credit added to client...', // not sure this would be used without testing
		'amountout' => $creditamt, // not sure if amountin or amountout is used. This would be passed in as delcared var
		'fees' => '0.00',
		'credit' => '1',

		);

		$addInvoiceCredit = localAPI($command, $values, $adminuser);