Sales order fails code 3008

We have the pro version, however, there is no contact name order field as per your documentation, there is an assign contact field which allows us to connect our contact feed, however we get the error in the log “Error Code 3004: message The Customer field can neither be blank nor be incorrect. Please enter a correct customer” I can see in the logs there is no contact data being passed on to zoho, how do we resolve this? our contact feed works fine and it is running prior to sales order creation, so the contact has been previously created. Thanks.