HTTP 400 error - It's not you, it's this link

Hello,

I am having an issue with a few users gaining access to a dashboard.

Here is the context:

Our company did a soft rollout of Power BI to a few select users to demo the functionality. For these users, we provided Pro Licenses to view a dashboard mockup. After demo/financing was approved, we opted as an organization to use the Premium service, and removed the pro licenses.

After the change the premium, the group of users who used to have Pro licenses are no longer able to access the same dashboard that they were able to view in the demo. They get a response that says HTTP 400 error, It's not you, it's this link (it appears to be broken). This problem affects users internal to our office network as well as external users with access. I have added new users since the change to Premium who are able to view the dashboard without an issue. Any ideas? Thanks in advance.