Using a custom field in Eloqua, can we fetch and also update the contact details using web services?

Using a custom field in Eloqua, can we fetch and also update the contact details using web services?

For eg, the custom field we want to use is "C_ID_Iqama_Number1"

We had tried to fetch the details of the contact using the below payload:

But could not retrieve all the contact details. Let us know if there is an API where we could achieve the above