A red circle usually indicates that there is no activity in the fitness application. If the application can't detect any motion data, it may be because some functions are not turned on or the equipment is out of order.
Here are some possible solutions:
1. Turn on the heart rate monitoring function: If the heart rate monitoring function is not turned on, the fitness application may not be able to obtain exercise data. Please make sure that the heart rate monitoring function is turned on and try to restart the device to see if the problem is solved.
2. Check the system problem: If there is something wrong with the equipment system, the fitness application may not work normally. Please try to update the iOS system, or wait for the system to return to normal. If the problem still exists, it is recommended to contact Apple customer service or go to after-sales service.
3. Check the phone screen: If the phone screen is damaged, the fitness application may not display the data normally. Please try changing the phone screen to see if the problem is solved.
If the above methods can't solve the problem, it is recommended to contact Apple customer service or go to after-sales maintenance.