Promotional banner is still showing up after you purchased a license
Most likely the license assignment failed or you purchased using a different account.
When you purchase a license for SecureMailMerge, you login to our licensing server with a Microsoft 365 account. This account is assigned the purchased license automatically if you only purchase one license. This may be right for your use case or you want to change the licensed mailbox.
Step 1.Login to the license server (login with the account you used to purchase the license)
You will be presented with the subscriptions assigned to your account. Click on "Assign Licenses" to add/remove/change the email addresses of the mailbox you want to assign the license(s) to.
Is the list of subscriptions empty?
This happens usually if you used an administrative (or other) account to purchase the license. Sign out of the license server and login again with that account.