When selecting on of the two aforementioned FSx type storage, it necessary to have a validation on the presence of a selected volume id. If a volume id is not selected, then it must not be possible to move on from the current step. Right now there is no validation on that selection, so when you go on and perform a dry-run you get an ugly text straight from a python exception from PC backend (see attachment).

Workaround
Just make sure to select a valid volume ID from the dropdown if there's any. Otherwise, don't use FSx storage.