Hello @AnnaAllschwil
Thank you for your question.
It really depends: differents error codes have different meanings but can mostly be solved.
Try logging out and back in in the App: if this does not work, delete the App and download it again.
If you still do not manage to solve the problem, check the FAQ here or fill out the form: SBB Mobile | SBB help & contact
You will be required to give information about your device (brand, model), about the App (version) and so on.
It is always helpful if you have a screenshot of the error as well.
I wish you a nice day
EleonoraS