To answer my own question, you have to provide the Screenshot and Review Notes in the Review Information for the In-App purchase to be eligible for preview. Once I filled both these fields, I was able to add them for Review. My mistake was that I didn't understand that these fields were mandatory.

The original works without problem but it is written in swift. It is the sample code from "Adjusting the brightness and contrast of an image" . I translated the code to obj-c myself, since I couldn't find an obj-c version.

Exactly.

Correct. The original uses: source.applyGamma(linearParameters: linearCoefficients, exponentialParameters: exponentialCoefficients, boundary: preset.boundary, destination: destination)

In case it helps: Stepping my app and the swift sample under the debugger I noticed something: for an 800x600 RGB image the function vImageBuffer_InitWithCGImage returns a vImage_Buffer with rowBytes=2400 in my obj-c app, instead of the expected 2432 that I get with the swift version. Inquiring about the imageAlignment I get the correct value of 64 in both apps.

Thanks Quinn, it finally works. Copying the logic from the swiftinterface for macOS I replaced viErr = vImagePiecewiseGamma_Planar8( &sourceVImageBuffer, &destinationVImageBuffer, expoCoeffs, gamma, linearCoeffs, boundary, kvImageNoFlags ); if (viErr == kvImageNoError) { CGImageRef newImgRef = vImageCreateCGImageFromBuffer( &destinationVImageBuffer, &invIFormat, nil, nil, kvImageNoFlags, &viErr ); with vImage_Buffer bufSrc; vImage_Buffer bufDest; bufSrc.data = sourceVImageBuffer.data; bufSrc.width = sourceVImageBuffer.width * img_bPP / img_bPC; bufSrc.height = sourceVImageBuffer.height; bufSrc.rowBytes = sourceVImageBuffer.rowBytes; bufDest.data = destinationVImageBuffer.data; bufDest.width = destinationVImageBuffer.width * img_bPP / img_bPC; bufDest.height = destinationVImageBuffer.height; bufDest.rowBytes = destinationVImageBuffer.rowBytes; viErr = vImagePiecewiseGamma_Planar8( &bufSrc, &bufDest, expoCoeffs, gamma, linearCoeffs, boundary, kvImageNoFlags ); if (viErr == kvImageNoError) { CGImageRef newImgRef = vImageCreateCGImageFromBuffer( &destinationVImageBuffer, &invIFormat, nil, nil, kvImageNoFlags, &viErr ); and it works for both monochrome and RGB images. Interesting trick to know. Many thanks again.

Thanks for replying Ed. I don't see anything suspicious in the Behaviors tab. I have never touched it anyway. The only thing I changed is the key for Pause/Continue in Debug menu from Cmd-Y to F5.