Answer to: How do I push back on an impossible scope?

Fact: There is a huge team somewhere creating this software that comes with a very expensive license. Fact: Your company thinks it can save money by creating a replacement for this software. Common sense: If you could do that then anyone could and the supplier would be out of business. Since you are posting on “workplace” and not “software development”: It is clear that you won’t succeed. So it is pointless to try too hard and stress yourself and wear yourself out. To make sure you get paid for the longest possible time, make optimistic noises, tell them “this will take longer”, not “this cannot be done”. Drag it out. Ask for a raise. If you get it, good. If you don’t, it makes you feel better about eventually failing. And at some point look for a job elsewhere.