Unable to connect to Homebase (-3)

Hi,
everything seems to working fine, until my mobile phone is out of wifi range, away from the home, and I want to see a notification received on my mobile phone. I click to view the video or answer the doorbell and I get the error message in the subject.

Why can my Homebase 2 not stream the video over the internet via 4G mobile data? where is the problem?

Thanks