WebSocket
1003 Unsupported Data
An endpoint received a type of data it cannot accept. For example, a text-only endpoint received a binary message, or vice versa.
When You See This Code
The client sent a binary frame to a server that only handles text, or a text frame to a binary-only endpoint. The receiver does not know how to process this data type.
How to Fix
Verify the message type (text vs binary) matches what the server expects. Update your client to send the correct opcode for the data format.