At this time the Age of Empires forums use a separate sign-in from the Age of Empires Insider Program, though this may change in the future.
🛠Create an Age Forums Account
If you have not done so, you will need to create an account for the forums using the same Microsoft account that you used to sign up as an Age of Empires Insider.
If you sign up on the forums with a different Microsoft account, you may notice irregularities such as your forum permissions and badge flair not aligning with your status as an Age of Empires Insider.