A free program from Microsoft that provides developers with the tools, resources, and sandbox environments needed to build solutions for Microsoft 365.
Workaround / Solution that worked for me:
If you get stuck when setting this up from the M365 Developer Portal, the actual fix needs to be done in the Azure Portal (not in the M365 Portal).
In my case, I had no active subscriptions associated with my Invoice Section. Here is the step-by-step process I followed to resolve it:
Sign in to the Azure portal (using an account with admin privileges).
Open Cost Management + Billing.
Go to All billing subscriptions (or Invoice Sections > Azure subscriptions).
Since there were no active subscriptions listed (0 subscriptions), I clicked "+ Add" to create an Azure subscription.
Once the Azure Plan / Subscription was provisioned (took a few minutes), the issue was resolved and I was able to proceed.
_Note: While there may be multiple causes for this error, hopefully this helps anyone facing the same situation!
_Note: that the credit card number entered under "Create a new billing account" is registered as the default payment method in the Azure Portal, and it appears that it cannot be detached.