Originally Posted by
abielp
Ah yes, I am already being asked to pay the express fare + seat reservation. I wonder if there is another way to reserve seats in advance.

My suggestion now would be to contact Fujikyu directly. They have an online “concierge” form.
https://www.fujikyu-concierge.com/contact_en/
The English language reservation option is relatively recent. It is simpler than it used to be, but the Tokyo Wide Pass Express Surcharge exemption may have been overlooked.