Hi,
If you look at the model trace, you will notice that the said process is associated with a model entity and not a transporter. Within the 'PickUp' step's advanced options, you have to specify transporter type and currently it is set to 'Associated Object' which in this case is a model entity. Since the Pick Up step is looking for a transporter you are getting this error. One solution is to define a 'transporter reference state' and then using an 'Assign' step at the beginning of the process assign 'vehicle', to it, this will assign the current vehicle to the 'transporter reference state'. Then change the 'Transporter Type' property of the 'Pick Up' step to 'Specific' and 'Transporter Name' to the 'Transporter Reference State' that you created.
Thanks,