Hi Scott Searcy,
I'm glad to hear that you were able to resolve the issue and thank you for sharing your solution so that others encountering the same problem can easily reference it! Since the Microsoft Q&A community has a policy that "The question author cannot accept their own answer. They can only accept answers by others ", I'll repost your solution in case you'd like to accept the answer.
Ask: While working through the prereqs for the App In A Day training session, I encountered an error while trying to add a Dataverse.
Solution: The error occurred because the Power Automate per user license (trial) had not been assigned. Once the admin added the necessary license and assigned it to the user, the issue was resolved, and Dataverse was successfully added.
If you missed any details or if you’d like to add more context, please feel free to comment below.
If you have any further questions or need assistance, don’t hesitate to reach out. Thanks again for your time and patience in resolving this issue.
Please don’t forget to Accept Answer and mark "Yes" for "Was this answer helpful" where applicable to benefit other community members.