Authorize LineItem's, mixed free and paid for causes error

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Unit Price of 0 causing problems in Authorize.net CIM lineitem

Today at work I ran into an interesting problem. The problem was this:

One of our clients has an ecommerce platform we built for them, as part of its backend, it uses Authorize.net's CIM service. Today and yesterday they happened to be running a free item. Besides the obvious server load funtimes to be troubleshot, there was a peculiar problem popping up. If someone tried to buy the free item and any other non-free item, the Authorize.net API would return this error message:

The element 'lineItems' in namespace
AnetApi/xml/v1/schema/AnetApiSchema.xsd' has invalid child element
taxable' in namespace 'AnetApi/xml/v1/schema/AnetApiSchema.xsd'. List
of possible elements expected: 'unitPrice' in namespace
AnetApi/xml/v1/schema/AnetApiSchema.xsd'.

Which seemed a bit odd. Why would the taxable element be messed up? It's simply set to false all the time. User's were checking out with the free item fine, and with paid items fine, but when combined into multiple line items this message appeared.

Troubleshooting involved playing around locally with removing the unit price and taxable fields entirely, getting a different error message. Good! This means that the problem does involve those two fields. Removing the taxable field didn't change the message, so it seemed the problem lay in the unitPrice being 0.

I checked out the schema from authorize and noted the following area:

<xs:restriction base="xs:decimal">
    <xs:minInclusive value="0.00"/>
    <xs:fractionDigits value="4"/>
</xs:restriction>

Well, I wondered, could it be that it is seeing 0 as a false value or something other than an integer? In this SO post someone noted that qoutes are a good idea, to which I tried and recieved a message about the format being invalid. So that was out.

Instead, I used sprintf to format the number into a decimal form so that Authorize's API wouldn't treat it as whatever it had been.

Old:

$lineItem->unitPrice = $item->price // is 0

Fixed:

$lineItem->unitPrice   = sprintf("%.2f", $item->price);

And lo' and behold. The transaction with a mixed set of items was processed succesfully!

Hope this helps anyone out there who runs into the same problem I did.

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