When one reads the rules for irresistible force (IF) and miscasts, the spell takes effect first and then the miscast is applied (top of page 34, CRB). The general FAQ reinforces this ruling on ToV as follows:
Q: If a Wizard casts Throne of Vines with Irresistible Force do
they get to ignore the miscast on a 2+ as the miscast occurs after the
spell is cast? (Reference)
A: Yes.
Now, coupled with the lizard FAQ on cupped hands, it is apparent that both ToV and its "save" are conducted first. Then, if and only if that save is failed would the cupped hands come into play since a successful ToV roll of 2+ means that any miscast is ignored and, in essence, doesn't occur.