I can't use skins in multiplayer mode

I bought some clothes to edit the character and I couldn't use them in multiplayer mode

[Step 1]
I started the game.
Click on Market
I clicked on the hamburger (3 horizontal lines) to expand the menu and selected "Go to dressing room"
On the left side of the screen, I clicked on the third icon – Hanger icon.
I expanded the menu, where it was "Classic Skins".
I clicked on Skins I Own to view my owned skins.

[Step 2]
When I select and equip the skin, it is equipped as if I were using it, but when I return to the game, it is not equipped.

Inside Minecraft, I recently went shopping for clothes. I realized that I couldn't use them in multiplayer mode, only in singleplayer mode. So I recently tried to add classic skins and saw that it wasn't possible either. Whenever I enter servers and try to equip some classic skins, my character still has Steve's skin.