You could put the video on Youtube and put a link on the forum. There is a decent chance readers here can help you figure out what is wrong. Fiverr gives you fairly generic answers, but some of the basics are (get ready for this long list):
file size too big or too small, video too long or too short, displaying content that is copyrighted (minions, celebrities, logos of companies), using video that is poor quality or low resolution, displaying something in your video that isn’t true like a level badge you don’t have yet, etc.
There used to be requirements that you have “exclusively on Fiverr” displayed as text in your video and also spoken in your video. They have relaxed those requirements now but some editorial staff might still deny a video over that.
You have to have some kind of sound with your video in the entire thing, but it can be royalty free music or spoken audio. You cannot use copyrighted music or they will deny it for that.