Of course you should not wait around. I think rather the opposite that the engineers should be more involved in working on the requirements. The issue is more rushing and being expected to magically just conjure something. Changing requirements is a fact you just have to live with in many industries.
Changing requirements is fine. Changing requirements when it was eminently avoidable is very, very bad.
If I asked you 6 months ago if you might ever consider something other than credit card payments, urged you to seriously consider this and you say no, you shouldn’t come to me now and say that bank transfers (bank transfers!) are absolutely indispensible.