template slice can only have 1 item, got 2

[state-developer]

Have an object defined like this:

var StatusMutation struct {
     StatusCheck struct {
          ID graphql.ID `graphql:"id"`
          ... 
          StatusHistory []struct {
               Status string `graphql:"status"`
           } `graphql:"statusHistory"
     } `graphql:"statusCheck(input: $input)"`
}

Here is the mutation:

...
  statusMutationInput(input: $input){
      id,
      statusHistory{
        	... on SubmittedEvent{
                    status,            
            },
            ... on FinalizeEvent{
                    status,            
            }
          }
...

This works perfectly if only 1 item is passed into the StatusHistory. However, if I get more than 1, I get the template slice can only have 1 item, got 2 error above.

Here is the error (with debug):

template slice can only have 1 item, got 2, Locations: [], Extensions: map[code:graphql_decode_error internal:map[response:map[body:{\"data\":{\"statusCheck\":{\"id\":\"dHJhbnNhY3Rpb25fNmswaGNwenY\", ... ,\"statusHistory\":[{\"status\":\"SUBMITTED\"},{\"status\":\"FINALIZED\"}]}},\"extensions\":{\"requestId\":\"810d4903-6e2b-4d6c-a6d6-82cf5e33f80a\"}}

We can get 0, 1 or all of these events.

Not quite understanding why this is happening if I'm allowing for more than 1 item to be queried?

Thanks.

EDITED: Forgot to include mutation*