@Iusta
Hi,
If the problem is that the camera shows the offline status on the Tapo app when you are using the mobile data on your phone, please help confirm the following information.
1. Please send me the MAC address of the camera. You can find its MAC address on the Tapo app>camera's Device Settings>Device Info page.
2. Is the camera connected to your router's Wi-Fi directly? Are the time and date correct on the camera's Live View page?
3. You can try to change the DNS server(change to 8.8.8.8 and 8.8.4.4) and disable the special settings, such as firewall, access control, etc., on your router.
If you have another issue, please describe it in detail for further help.
Best Regards