Well, I cannot exclude the error 400 gets the priority before 403 (though I'd expect the opposite), so this test is not conclusive. You best contact the Customer Support, send them the screenshots with the errors, and have them investigate it.
You mean you get also the error 403, while connected to the WiFi router, and syncing normally while on mobile data? Or do you mean just that you cannot sync? In the later case, there may be hundreds of other reasons for the failed syncing. If you did not do it yet, check also your Device Sync Audit - it may reveal more about the exact reason.
Hi since yesterday only me and my wife's garmin devices synced with garmin connect while our phones are connected to the home wifi network, I synced my device just now and it stil works this morning
