chore: handle NumberFormatException

Description

This MR handles NumberFormatException in case a response from API couldn't be parsed to an integer.

Issues

https://gitlab.e.foundation/e/os/backlog/-/issues/2299?show=34866

10 commandments of code reviews

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Summary by CodeRabbit

• Bug Fixes
  • Improved error handling in the invite sending process to prevent crashes from unexpected string formats.
  • Enhanced robustness by returning -1 for invalid error codes instead of throwing exceptions.