I am making Photo Extension, but when I am trying to save changes(Done button Tapped).
Alert Message Says "Unable to Save Changes" - 'An Error occurred while saving. Please try again later.'
This is my code for finishContentEditingWithCompletionHandler:completionHandler
- (void)finishContentEditingWithCompletionHandler:(void (^)(PHContentEditingOutput *))completionHandler {
    // Update UI to reflect that editing has finished and output is being rendered.
    // Render and provide output on a background queue.
    dispatch_async(dispatch_get_global_queue(QOS_CLASS_DEFAULT, 0), ^{
        // Create editing output from the editing input.
        PHContentEditingOutput *output = [[PHContentEditingOutput alloc] initWithContentEditingInput:self.input];
        NSURL *originalImageURL = self.input.fullSizeImageURL;
        //Apply filter
        CIFilter *appliedFilter = [CIFilter filterWithLUT:self.presetFilterNameArray[self.currentAppliedFilterIndex] originalLUT:@"LUT-ORG-512" dimension:64 alpha:self.filterAlphaSlider.value CIContext:self.ciContext];
        UIImage *filteredOriginalImage = [self filterApply:[UIImage imageWithContentsOfFile:originalImageURL.path] filter:appliedFilter];
        //Apply orientation
        filteredOriginalImage = [UIImage imageWithCGImage:filteredOriginalImage.CGImage scale:filteredOriginalImage.scale orientation:self.input.fullSizeImageOrientation];
        // Provide new adjustments and render output to given location.
        NSData *archiver = [NSKeyedArchiver archivedDataWithRootObject:self.presetFilterNameArray[self.currentAppliedFilterIndex]];
        output.adjustmentData = [[PHAdjustmentData alloc] initWithFormatIdentifier:@"com.fantagram.BetterAndBetter.TKPhotoExtension" formatVersion:@"1.0" data:archiver];
        NSData *renderedJPEGData = UIImageJPEGRepresentation(filteredOriginalImage, 1.0f);
        if([renderedJPEGData writeToURL:output.renderedContentURL atomically:YES]){
            NSLog(@"success to write");
        }
        else{
            NSLog(@"fail to write");
        }
        NSLog(@"%@", output);
        // Call completion handler to commit edit to Photos.
        completionHandler(output);
        // Clean up temporary files, etc.
    });
}
Previous Answer for this issue, someone said that when rendering to NSData, the size of image need to be different with originalImage. So I tried this, but didn't work.
One More Thing.
Are there any way to open the host app from photo extension?
self.extensionContext openURL: didn't work(As I know of It only works in Today Extension.)
UIResponder *responder = self;
        while(responder){
            if([responder respondsToSelector:@selector(openURL:)]){
                dispatch_async(dispatch_get_main_queue(), ^{
                       [responder performSelector:@selector(openURL:) withObject:[NSURL URLWithString:(MY_URL_Schemes)]];     
                });
            }
            responder = [responder nextResponder];
        }
above code also didn't work. It worked when I used it share extension.
Thanks.
                        
Try this,
Go to SETTINGS then PHOTOS & CAMERA. I changed the options from Optimize iPhone Storage, to DOWNLOAD & KEEP ORIGINALS.
I think Normally under the Optimize setting photos are downloaded back to the original and then you are allowed to edit.
Hope it will help you.