Too hard to point out artifacts at this resolution. However, you must view the image at least 100% to check carefully for such things. I think if you look at the edge of the glass - for example - you may see the pixels being a bit 'blocky'. If so, this would be due to JPEG compression and therefore the artifacts rejection reason.
Did you take this in raw format or JPEG? Did you use a smartphone? Generally speaking, if you want to upload to Adobe Stock, you are better off using raw files, post-process to a degree using raw software and then convert to JPEG using the highest resolution.