Payment is not switched on
There is no payment provider connected to this app. Nothing is charged, no card details are asked for or stored, and no subscription starts. Everything in every plan is open to you today.
Access stays free and complete while this is the case. Nothing here can restrict you.
You haven't picked a plan
That changes nothing about what you can use. Everything is open while the product is being built.
Where your commercial state stands
Plan, payment, code, entitlement and actual access are separate things. They are kept apart here so nothing reads as more real than it is.
Change what you noted
Moving up or down is a change of intention today, not a billing event. Nothing is prorated, nothing ends.
When billing goes live
Nothing starts on its own. You will be asked again, shown the full price with tax, and only then can anything be charged.
Plans are described in full on the pricing page.