I cannot switch between worlds on my Minecraft realm.

When I try to switch between worlds on my Realm, I got an error.

I was expecting to be able to switch between worlds on my Minecraft realm.
I thought it would work usually as intended.

Instead I got an error.
When I tried to switch between worlds in my realm, I noticed it wasn't working, and then after a while, I got red text in the bottom that said - 504.

Steps to Reproduce:
1. Click on the "Realms" button in the Minecraft main menu.
2. Select your realm.
3. try to switch your world on your realm.
4. Wait a while.
5. You should get something that says - 504.