Tag manager API trigger creation 500 errors

[howlCode]

We are experiencing an issue with the Google Tag Manager API method to create a trigger which has suddenly started to give 500 status with the message "Experienced an internal error". We can't seem to find a team that handles this API directly and so we'd appreciate if you could help us find the correct support route. This issue appears to be triggered when using either the ruby gem or posting to the API directly with a rest client. It was working fine until late last month AFAICT.

• This is the route we are using: https://developers.google.com/tag-platform/tag-manager/api/v2/reference/accounts/containers/workspaces/triggers/create

• and this is an example of the request we are making though we have tried many different combinations and experienced the same error:

POST https://www.googleapis.com/tagmanager/v2/accounts/{ACCOUNT_id}/containers/{CONTAINER_ID}/workspaces/{WORKSPACE_ID}/triggers?access_token={ACCESS_TOKEN}

Authorization: Bearer {ACCESS_TOKEN}
Accept: application/json
Content-Type: application/json

BODY
{
  "name": "H&D Event Category",
  "accountId": "{ACCOUNT_ID}",
  "containerId": "{CONTAINER_ID}",
  "workspaceId": "{WORKSPACE_ID}",
  "type": "customEvent",
  "customEventFilter": [{
    "type": "equals",
    "parameter": [{
        "type": "template",
        "key": "arg0",
        "value": "{{_event}}"
      },
      {
        "type": "template",
        "key": "arg1",
        "value": "gaTriggerEvent"
      }
    ]
  }],
  "filter": [{
    "type": "contains",
    "parameter": [{
      "type": "template",
      "key": "arg0",
      "value": "{{gaEventCategory}}"
    }, {
      "type": "template",
      "key": "arg1",
      "value": "Hours"
    }]
  }]
}