Dorota P. couple of potential issues - one is that I would make sure you duplicate our Relume Figma Kit and import your wireframes into that duplicate.
If that doesn't work or if you are already doing that, then its possible that its the language and you may need to use english initially. I'm hoping thats not the case though.
If that is the case, can you let me know which language it is you are trying to use to import wireframes?