Kiato-Patra(s) Seat Reservations

Hi all

We want to travel Athens to Patra April 5th. We have Global pass (2 month 1st class)

We know its a train from Athens to Kiato then Bus connection from Kiato to Patras.

Both Interrail app and Hellanic train website state seat reservation is compulsory for bus section.

We believe as this is a train-related bus transfer, the bus section should be free using our interrail pass

There appears to be no Online method of making this seat reservation without paying.

Is the ONLY way to make this seat reservation to go in person to the train station in Athens?

Thank you