Exception: acados acados_ocp_solver returned status 4

Hi, I have trouble designing a tube MPC using Acados. I need to design a tube MPC for my thesis and wanted to approach this by first implementing a very rudimentary tube MPC in Acados to get a feeling how to do things in Acados.
Most errors I could fix by searching the source code to find out what happens, but the status generation cannot be found in the source code.

I got the error: Exception: acados acados_ocp_solver returned status 4

Therefore, my question is: What does status 4 even mean?

And by that note, is there some documentation what any status means? On https://docs.acados.org/python_interface/index.html, there is no explanation.

I was able to avoid the status 4 and make the system run by making the constraints more generous, i.e. giving the controller more “space”.

Thank you for your answer

Here are two relevant threads about infeasibility issues:

I suggest to look a bit more into existing posts.