Firstly, it could indeed be a format or size restriction on the platform. Even though 2.5 MB doesn't sound like much, some platforms have surprisingly tight restrictions. The format being mp4 should generally be okay as it's a widely accepted format, but again, platform specifics may vary.
You might want to try converting the video to another format or reducing its size just to see if that helps. If you need a good tool for that, check out this article at [movavi.com] , which gives some solid recommendations for free editing software. You could use one of those tools to adjust your video to meet the site's requirements, if that turns out to be the issue.

If you've tried all of this and it's still not working, reaching out to customer service would be your best bet. They should be able to give you the specific requirements or troubleshoot the issue further.