Magento 1 api qty_invoiced decimal

Importing a sale from a 3rd party using SOAP and the quantity parameter always ends up in the Magento completed order rounding up to whole number. Selling in kgs. The following

$xmlRequest .=  "<quantity>".number_format($resultSalesOrder[items][$j][qty_invoiced])."</quantity>";

Produces

<quantity>0.6000</quantity>

But in Magento order qty is 1.

Do I need to add a decimal point to the .number_format?