This is the email reply I received from Amazon:

Your Brand Registry enrollment application has been rejected.

Why did this happen?

Please note that the USPTO requires foreign domiciled applicants or registrants to be represented by a U.S. licensed attorney. This rule was designed to improve the quality of trademark submissions by U.S. attorneys who are bound by ethical rules to follow the USPTO rules of professional conduct and their state bar codes of conduct. Attorneys suspected of misconduct may be investigated by the USPTO. If you are working through an intermediary, rather than directly with a US licensed attorney, to seek a US trademark registration or enrollment into brand registry, your application may be subject to additional scrutiny by Amazon and the USPTO. Before hiring an attorney or a trademark service company, check whether they are subject to an Order for Sanctions from the USPTO or listed as an entity on the Potentially Misleading Solicitations webpage. If you are concerned about the validity of your application or the conduct of any of the entities involved in your application, consult with a private U.S. attorney who is knowledgeable about trademark law (and not connected to any entity listed on the Order for Sanctions or Potentially Misleading Solicitations webpages) to evaluate your application. You can also go to Amazon IP Accelerator website to learn more on how it helps connect you with a curated network of trusted IP law firms