New to API, 403 Errors

I’ve created a few admin users and verified them against the api using a get request for site settings:

curl -X GET "https://my.discourse.com/admin/site_settings.json" -F "api_key=theGeneratedAPIKeyForanAdmin" -F "api_username=anAdmin"

This returns the site settings, However attempting to add a user to a group or even add a topic fail with the same api users.

For instance:

curl -X POST "https://my.discourse.com/posts" -H "Content-Type: multipart/form-data;" -F "api_key=theGeneratedAPIKeyForanAdmin" -F "api_username=anAdmin" -F "title=This is an API created topic" -F "topic_id=38" -F "raw=This is the end of the world as we know it, and I feel fine."

returns:

{"action":"create_post","errors":["Something has gone wrong. Perhaps this topic was closed or deleted while you were looking at it?"]}

I’ve left category, target_usernames, archetype, create_at out of the curl command as they’re optional (according to the api docs).