Can you give the actual rejection reason? Was Artifacts problem, Technical Issues...I think you have a problem with your white balance...also with noise - both colour and luminance.
Yes, white balance and noise (luminance and colour).
In addition to what Ricky highlights, more depth of field is needed. The right side of the image, especially the lower right, don't seem to be sharp.
When submitting an image featuring a common subject such as a flower, sunset, house pet, etc there needs to be a major WOW factor to it to be considered. At first glance, the image appears to be a bit underexposed and lacks contrast. It's an OK photo of a common subject and unfortunately, OK isn't good enough for this type of content. There is a market for these images but there are a lot of them already in the database.
If this were my image and I had a RAW file for it I would bump the exposure, increase the contrast and vibrance. I don't think it will go through even with those changes but that's where I would start.