Use a sanding sponge in the 180-grit area. It’ll be tedious, but you’d be surprised how little a ridge will show through to new paint film!
* Make sure you prime after all the sanding! Remove all dust first, then prime.
* Once the primecoat is dry, inspect wall very closely, at different angles, to find other flaws/ridges leftover. Repair/sand again as needed, and brush on a hazy coat of primer on these areas.
* Finally…ready for 2 full coats of paint!!
Faron