The Mixer Error: "Uh oh, it seems like you're hitting our API rate limit! Please wait a bit before trying again." is caused by attempting to view or change a Mixer setting more frequently than is allowed.
For example: changing your name can only be done every 30 days (whether you make the change through the UI or through the API).
Developers may want to read the section on "Rate Limiting" in the Mixer API Documentation for a complete list of items that can be requested or changed in Mixer per time interval.