I don't know if this is the right place to ask but just about an hour and a half ago I donated to optifine to get a Minecraft cape and when I join Minecraft both single player and multiplayer the cape simply will not appear on my back. I even restarted the game and asked people on the hypixel server if they could see my cape and they all said no. I've been searching all over the internet for help and the things I found didn't work, like toggling capes on in the video settings. one website said I should change my optifine cape and it might work but when I DO try to change my cape on the optifine website it says that the password is invalid even though I know with 100% certainty that the password is correct, I even went to my email and found the email receipt I got for the payment going through and I checked my bank account and saw that the money had come out so I definitely paid for it. the optifine website doesn't specify whether it needs my Minecraft password or my email password either btw and I tried both passwords and it was STILL invalid.
Optifine capes can only be seen with the Optifine version of Minecraft (or the Forge version with Optifine loaded), because it's not an official cape by Mojang. It's not saved on your account, but instead the Optifine version of Minecraft checks on Optifine's servers for a cape.
So of course other players can't see your cape and you can't either, unless they or you play with Optifine.
Also maybe it takes a little while for them to process your donation. Try again in the next few days (maybe it requires manual action and the people don't work on the weekend) and if it's still not there then, contact them and ask if it's finished processing.