Spring 'Sec-WebSocket-Accept' value incorrect - spring

Question

When connecting to a WebSocket from my frontend (using Stomp for Dart):
client = await connect(uri);
The client sends this key in the header:
Sec-WebSocket-Key: ydWCNEacB1ZqiHCH1Ip+vo4mhOw=
And receives a key back from the Spring WebSocket:
Sec-WebSocket-Accept: KVqExHty0Y5/fze11/EAhg==
This causes the client to throw:
WebSocket connection to 'ws://user:pass#localhost:8080/ws'
failed: Error during WebSocket handshake: Incorrect
'Sec-WebSocket-Accept' header value
I don't know how to calculate the correct response. But either way the client doesn't accept it for some reason.
How do I approach this problem? What could be causing the problem and how might I solve it?
Thanks
Edit: added websocket config:
#Configuration
#EnableWebSocketMessageBroker
public class WebSocketConfig implements WebSocketMessageBrokerConfigurer {
#Override
public void configureMessageBroker(MessageBrokerRegistry registry) {
registry.setApplicationDestinationPrefixes("/app").enableSimpleBroker("/topic");
}
#Override
public void registerStompEndpoints(StompEndpointRegistry registry) {
registry.addEndpoint("/ws").setAllowedOrigins("*");
registry.addEndpoint("/ws").setAllowedOrigins("*").withSockJS();
}
}
Also
#Configuration
public class WebSocketSecurityConfig extends AbstractSecurityWebSocketMessageBrokerConfigurer {
#Override
protected void configureInbound(MessageSecurityMetadataSourceRegistry messages) {
messages.anyMessage().authenticated();
}
}
Edit: I found a wiki that describes how to calculate 'Sec-WebSocket-Key'. Following the guide below, it does look like the key is incorrect. This doesn't seem likely though or many more would be having issues.
https://en.wikipedia.org/wiki/WebSocket