Halide might fail to save a photo and show the error, "Error Saving Photo — An error occurred while saving your photo. Details: (The operation couldn't be completed. PHPhotosErrorDomain error 3301.)"
We understand this is a terribly frustrating message to get. This error is caused by a problem in Apple's Photos framework in iOS and beyond our control. It is impossible to fix this, and it affects many more apps than Halide.
The issue has been reported to Apple, and should be fixed in a future update to iOS 15. However, to help Apple, it's helpful to submit a bug report yourself with diagnostic information, you can do this through their Feedback Assistant Website.