Permanent residence (PUT) — how long does the employment contract need to be?

Hey everyone, for my friend, we are trying to understand how Migrationsverket evaluates the income when applying for permanent residence. The rules seem unclear. Some people say you need at least 18 months left on your contract but some other people seem to have received it with shorter contracts.

Has anyone here recently gone through the process or appealed a decision on these grounds? How long was your contract, and what kind of documentation did you provide to show that your employment was considered stable?

Would really appreciate hearing about your experiences or any advice on this matter.