From what it seems, your application is under the developer license, which means that you are allowed a maximum of 5 OAuth tokens and since your application is exceeding this, you are receiving this message, which is the expected behaviour.
Can you confirm?
Also, if your applications happens to be under developer license, you might have recived an email quoting this:
When development is complete, you can schedule a demo with the Twitter Ads API team at t.co/meeting. We will be looking for a functional, attractive design that meets all terms described in the Ads API Developer Agreement. For partners with write permissions, we will be confirming that the full campaign management workflow (creation, editing, and reporting) is present supporting the products and campaign objectives that are important to the partner’s clients. Full API parity is not required.
Which is what you would want to do if you want to upgrade access.
