Hello guys im new to pixel joint, i tried to change my avatar and i notice that i can upload an image made by me and can use it as an avatar, but after i uploaded the image i get a message that it doesn't meet the quality standards or the art needs revision for miscellaneous reasons, mm i really don't know why i get that message, also im pretty new to pixel art, so any advice i would really appreciate it, thanks for your time!!.

(Hope this is the right place to post this O_OU)

This image, right?

The main problem is that you rescaled this art unevenly. Some "pixels" are bigger than others.
Another major problem is that you have icky lines that double up in thickness in corners. See how the bottom outline of the slime (and most of the top, in the first few frames) is made out line segments that don't directly touch each other? Do that for the rest of it, it makes a much cleaner-looking line.

It might also help to not pre-zoom the art. This isn't required by the rules, but unless your piece only makes sense at a higher zoom, it's best to upload at 1x and let the viewer choose the zoom. Without the pre-zoom, this'll fit as your avatar, too!

This isn't a rejection reason, but you could also improve the animation.
There's no sense of "squish" to the slime, because its volume appears to change between frames.
- The slime should probably get wider in panel 3 since it gets squished against the floor.
- The slime should probably get more flat/squat in panel 4, since that material is being pushed up out of it with the "flaps" at the top.
- The slime shrinks in volume in panels 5 and 6. It'd help to keep the volume looking more consistent.
- The jump between frames 6 and 7 is too great and feels choppy. This should be less of a problem if you don't have the slime shrink so much in the previous panels, but if it doesn't help, you could add another frame.