Did the rejection say "artefacts", exactly and only? Please check the words used in the rejection and tell us.
Thanks for giving us the chance to consider your image. Unfortunately, during our review we found that it features excessive post-processing and/or noise, so we can't accept it into our collection.
Excessive artifacts/noise can be caused by low light, bad camera settings, strong compression or excessive post-production.
If it was due to post production effects, know that our customers typically prefer to add their own special effects, filters or black-and-white conversions to fit the needs of their projects, so adding these effects in advance drastically reduces the market for your image.
Did you rework the background?
The file has been edited and you did not pay enough attention to the details.
But the image has also different other problems like sharpness, colour correction, exposure. I don't see this image passing.