WSDL-service throws ProtocolException: (402) Payment Required

Trying to reach the WSDL service ( through a visual studio project service reference I am getting a ProtocolException: (402) Payment Required.

The used method is FindFlight with the following parameters:
origin: “VKO”
destination: “LED”
include_ex_data: true
type: “auto”
filter: “all”
howMany: 15
offset: 0

The account’s billing settings seem to be correct, what could be the problem?

The “include_ex_data” argument is not eligible to be true when used with a Starter plan.