Hello alex.konstantinou,
Is this a bicycle or motorcycle you're using?
While the title of this page may not directly match, it will have some information on there that can help with this situation: If you can't make or receive a FaceTime call on your iPhone or iPad - Apple Support
For example, it'll help to note:
If your cellular connection or Wi-Fi network runs slowly, or other users stream audio or video on the same Wi-Fi network, you might have these issues:
•Connection alerts or unable to connect
•Choppy video calls
•Black screen
•Dropped calls
Make sure that both you and the person that you call use a fast Wi-Fi or cellular connection. If you use Wi-Fi, FaceTime requires a broadband connection.
You may try testing the FaceTime call while both users are on a fast, reliable Wi-Fi connection, and see if this has helped, as it can help rule out issues with the existing connection.
Cheers.