"createTransactionRequest” has invalid child element “clientId”

[NinjaJoe]

I have set up Authorize.net to accept payments from my web app. But after submitting a test payment, the response from Authorize.net is:

The element 'createTransactionRequest' in namespace 'AnetApi/xml/v1/schema/AnetApiSchema.xsd' has invalid child element 'clientId' in namespace 'AnetApi/xml/v1/schema/AnetApiSchema.xsd'.

List of possible elements expected: 'merchantAuthentication' in namespace 'AnetApi/xml/v1/schema/AnetApiSchema.xsd'.

What could be causing this error? Is there any solution?

[mmcguire]

The error indicates that clientId is present in the request and may not be in the right place. A sample request from your logs would help us to troubleshoot this issue for you.