Why I can't see my players skin ?

First, ensure to set the parameter 'server_online_mode' accordingly to the current online-mode status of your server.

Then, here is a double-entries table to understand how it works :

Your server online mode → Player client ↓	1	0
Bedrock Edition	✅ The player skin should be displayed perfectly. Geyser MC is assigning UUID to Bedrock players in order to allow us to get their skin with the Tydium API	❌ In offline mode, UUIDs are generated locally and can't make us identify a player. Even with the username of this player, we cannot get his skin. That's why you will see a bedrock skin.
Java Edition	✅ The player skin should be displayed perfectly.	✅ Even if the server is in offline mode, Java players skin can be get from public Mojang API. First we convert the username into the official UUID, then we get the user skin and display it on the dashboard.