Based on comments and many articles I have read, this is a common issue among Android and iPhones. The most common is your device may not be equipped with a Gyroscope.
You can detect if your phone contains a Gyroscope via this app Sensor Kinetics (Android). I am not an Apple device owner, so I do not know any Apple version of the app. If your device is compatible with a Gyroscope, many say that a possible solution is to enable your auto rotation.
Unfortunately there is no way to install a Gyroscope into your device, this is only done during the manufacturing period. I have checked if an app-based Gyroscope will work, but Pokemon Go requires a built-in Gyroscope
Problem #9: "Cannot detect your phone's orientation"error when switching to AR mode.
This is a problem a few of our readers recently reported. Searching the web it appears the issue could be one of two things:
Android - your phone may not have a gyroscope. If so, AR mode will not work. A few phones reporting this issue are Sony Experia, HTC 626S and all Huawei smartphones.
iOS - iPhone users with the iOS 10 beta 2 installed are also reporting problems with the phone detecting orientation for AR mode.
Yes you need to have a gyroscope in your phone if you want to use the AR cam. Meaning if you want to see the Pokemon with a real life background, you need a gyroscope.
The game itself will still work without a gyroscope, you'll be able to see the Pokemon with its animated background, just the AR (real life) camera won't work.
Pokemon GO – Problems & Solutions
Problem 10 – AR Mode/Camera Not Showing Pokemon
For many of you, when you toggle on AR Mode or the Camera, the Pokemon is no longer visible. You try to turn around to search for it but you still can’t find it. This totally removes the augmented reality experience that Pokemon GO has promised to deliver.
So what’s the solution? For now, you can play by turning off the camera (AR) mode to see the Pokemon. This problem seems to affect older devices that lack Gyroscope more often but there are records of it affecting new devices as well. Some people reported new devices like the iPhone 6S for this problem and such devices might have a faulty Gyroscope.
This problem may be fixed with an update from Niantic, so it is not entirely your device’s fault. Some who did experience this problem reported that by restarting the device the issue was solved. However, it does not work for everyone. Note that not everyone affected by it lacks a Gyroscope, this can be a compatibility issue and Niantic will have to address this in a future update to render the game compatible with your device.
If your phone is equipped with a gyroscope, then your issue may be something different (such as compatibility or older OS). For an issue such as this, Niantic may release further information and updates in the further.
Pokemon GO common issues
Pokemon GO camera not working
This is a similar issue to the “orientation” issue listed above, in that it’s generally related to your phone not supporting gyroscope technology. However, in some cases people are reporting that they still can’t access Pokemon GO‘s AR features even with gyroscope. This appears to be a not-so-common bug that is affecting older phones that support AR. For iPhone 6+ users, this could also be related to iOS 10 beta 2. It appears to be a bug and may be addressed in future updates.
If you are an Apple device owner running iOS Beta 1/2, reverting back to an older version may be a solution
Pokemon GO AR Mode not working
A number of players using iOS 10 beta 1/2 are reporting issues related to their phone not detecting orientation for AR mode. If possible, uninstall iOS 10 beta 2 and revert back to an older OS.