I’m trying to connect to AWS MQTT3 via websockets with authentication from Cognito, but I’m getting Caused by: software.amazon.awssdk.crt.mqtt.MqttException: The connection was closed unexpectedly.. What might be the problem?

This is my method for getting GetCredentialsForIdentityResponse

    public GetCredentialsForIdentityResponse getCredentialsForIdentity(AuthenticationResultType accessToken, String identityId) {
        try (var client = CognitoIdentityClient.builder()
                .region(Region.of(region))
                .build()) {
            return client.getCredentialsForIdentity(
                    GetCredentialsForIdentityRequest.builder()
                            .identityId(identityId)
                            .logins(
                                    Map.of(
                                            "cognito-idp.eu-central-1.amazonaws.com/eu-central-1_XGRz3CgoY",
                                            accessToken.idToken()))
                            .build());
        }
    }

After this I’m using GetCredentialsForIdentityResponse to obtain MqttClientConnection:

public MqttClientConnection buildConnection(String prefix,
                                            String region,
                                            String clientId,
                                            GetCredentialsForIdentityResponse credentialsForIdentity)  {
    try (var builder = AwsIotMqttConnectionBuilder.newMtlsBuilderFromPath(null, null)) {
        MqttClientConnectionEvents callbacks = new MqttClientConnectionEvents() {
            @Override
            public void onConnectionInterrupted(int errorCode) {
                log.error("Connection interrupted: " + errorCode + ": " + CRT.awsErrorString(errorCode));
            }

            @Override
            public void onConnectionResumed(boolean sessionPresent) {
                log.error("Connection resumed: " + (sessionPresent ? "existing session" : "clean session"));
            }
        };
        return builder.withEndpoint("%s-ats.iot.%s.amazonaws.com".formatted(prefix, region))
                .withWebsockets(true)
                .withConnectionEventCallbacks(callbacks)
                .withWebsocketSigningRegion(region)
                .withClientId(clientId)
                .withWebsocketCredentialsProvider(
                        new StaticCredentialsProvider.StaticCredentialsProviderBuilder()
                                .withAccessKeyId(  credentialsForIdentity.credentials().accessKeyId().getBytes(UTF_8))
                                .withSecretAccessKey(credentialsForIdentity.credentials().secretKey().getBytes(UTF_8))
                                .withSessionToken( credentialsForIdentity.credentials().sessionToken().getBytes(UTF_8))
                                .build())
                .build();
    }
}

and then when I’m trying to connect I’m getting previously mentioned error:

MqttClientConnection connection) throws ExecutionException, InterruptedException {
    try (connection) {
        CompletableFuture<Boolean> connected = connection.connect();
        boolean sessionPresent = connected.get(); // <--- here!
    }
}