Hi David,
When creating database using the portal, if you don't see the "Want to try Azure SQL Database for free?" at the top of Basics tab, scroll down a bit and select the existing logical server (that uses Free tier) again. This will normally make the banner appear so that you can click Apply offer button.
For example, if the Server dropdown already has the correct Free tier logical server, click on the dropdown, then click the server name in the dropdown, and finally the banner should show up at the top.
In example screenshot below "freetierserver" is already selected, but to get the banner to show up, we first need to click the dropdown, then click on freetierserver (West US).
Please click Accept Answer and upvote if the above as helpful.
Thanks.
-TP