PHP Soap Request标头与变量无法正常工作？

Question

I've been trying to create a concatenated url to use in a SOAPAction POST using php curl.

I've encountered an intersting issue with the SOAP Api i'm trying to access.

If i use the httpheaders array as:

$header = array(
    "Content-Type: text/xml",
    "SOAPAction: http://tempuri.org/IProductsService/getProduct"
);

I have no issues. It goes through and the response is exactly what i would expect.

However, if i use it like this:

$A = "ProductsService";
$B = "getProduct";
$soapAction = "SOAPAction: http://tempuri.org/I" . $A . "/" . $B;

$headerTest = array(
    "Content-Type: text/xml",
    $soapAction
);

It doesn't work. (yes there is an I on the soap action i need to use) I've tried various different ways of doing this. With soap action in the array, without soap action in the array. Syntatically in PHP it IS correct. However i keep getting the response from the api stating "ActionNotSupported". It says it cannot be processed due to a contractFilter mismatch at the endpointDispatcher.

Does anyone know why? And what i might be doing wrong?