I've encountered some difficulties with the Lufthansa app lately. It used to function smoothly for check-ins, bookings, and even flight changes, but since the latest update, I've been experiencing issues. Interestingly, I'm facing similar errors with other apps like Expedia and various car rental apps. As a workaround, I've resorted to using their mobile website instead:
https://veico.com/renta-de-autos-en-guadalajara/. It's been a helpful solution for me