If an NPC spawns with the default appearance, confirm that Citizens supports the running server build. Then check whether it affects one NPC or every player-type NPC.
Apply a known skin to a test NPC
Select a player-type test NPC. Look at it if needed, then replace the example name with a Java account that has a skin. Confirm the command targeted the intended NPC.
/npc select
/npc skin OyuncuAdi
Return to the NPC and compare it from a second Java client. If only one client fails, compare client conditions. If everyone sees the default skin, check Citizens and any skin plugin logs for the same attempt.
If Java and Bedrock differ, verify the Java appearance first and diagnose the Geyser rendering path separately.