I have six years' experience in marketing and four as a PMM. I am currently looking for my next challenge as a PMM and I keep failing the interview. As a result, I wonder how and what I should do in order to prove my value and pass my assignments.

Hello! I would encourage you to ask for feedback in the interview follow-up to understand where things are misaligned. In general I hire for:

Aptitude, Attitude, and Coachability.

If you are showcasing your empathy, curiosity, and prowess for the assignment at hand you will strike a positive chord with the hiring team. I'd also suggest having conviction in your point of view as many companies want PMMs to influence and incite change.

Make sure you do your homework and prepare compelling questions that showcase you're able to suss out unique solutions to complex problems.