"Bad Request" when trying to change skin

I tried to change my skin yesterday, and unfortunately, it did not work. I even clicked 'change' on the 'change my skin' page and it said 'Bad Request'.

I was already on Minecraft when I changed it (or attempted to) but on the title screen. It didn't work, I tried three times.

Earlier I tried again, before opening Minecraft at all, and still no success.

Can anyone help fix this?