Hello there aliffimran99,
I understand you're looking for help with your camera being unavailable while using SharePlay, so let's check into this.
While I understand you mentioned that you updated to the latest iOS version, let's just double check that you do have iOS 15.2 installed currently. If you do see that this is available to install, be sure to complete a recent backup. If you need assistance with either of these steps, check out the following resources:
How to back up your iPhone, iPad, and iPod touch
Update your iPhone, iPad, or iPod touch
Once you have confirmed that you're updated to iOS 15.2, let's review the following resources just to be sure the same steps are being taken when using SharePlay. In addition to this, check to see if your friend is able to see you although you can't see yourself just to confirm if the message may be incorrect.
Share your screen in FaceTime on your iPhone or iPad
Use SharePlay to watch and listen together in FaceTime on iPhone
If you see that the same steps are being performed and that you're up to date with iOS, it would be best to Contact Apple Support to look into this in more detail.
Have a great day!