How to add a SQS DeadLetterQueue?

Serverless Framework
1

I have set this in the main yml file:

resources:
  Resources:
    DeadLetterQueue:
      Type: AWS::SQS::Queue
      Properties:
        QueueName: test-DeadLetterQueue

It creates the sqs on a full deploy. But how to i add this Queue to a function?

With

onError:
Ref: DeadLetterQueue
I get an error:

validation error detected: Value ‘https://sqs.xxxxxx/test-DeadLetterQueue’ at ‘deadLetterConfig.targetArn’ failed to satisfy constraint: Member must satisfy regular expression pattern: (arn:(aws[a-zA-Z-])?:[a-z0-9-.]+:.)|().

Now, if i try to attach the queue like this:

resources:
  Resources:
    MyFunctionLambdaFunction:
      Type: "AWS::Lambda::Function"
      Properties:
        DeadLetterConfig:
          TargetArn:
            "Fn::GetAtt":
              - LambdaFunctionDeadLetterQueue
              - Arn

I get another error. (somethitng about a key, very generic) Why is this so hard to set up?