what is under the floor - basement-crawl space-slab?

By "flooring compound", is he talking about putting some kind of substance ON your floor to level it?

I'm thinking foundation issues. Check your basement floor & support beams. Hold a level to your basement ceiling joists and along the support beams. Minimal uneven areas might be ok, but if that bubble is way off the mark....support beams are likely the problem...or actually, the foundation below them.

its a two storey house with a basement foundation, and yes by flooring compound he means the cement auto levelling stuff

that does not sound right to me. I would rather find the cause.

If joists are sagging, adding compound (mass) to the top is going to be a temporary fix and will exacerbate the problem. Find out what's really going on and fix it if it needs to be fixed.