Website with Power BI unable to see Group/Workspace

Question

I am a Power BI/SQL developer who has inherited a website that integrates with Power BI using C# APIs. This has been working fine until today - whenever I attempt to load a Power BI report from the website, it throws an exception which I've tracked down in the code to here:

        var groupId = (await PowerBIClient.Groups.GetGroupsAsync()).Value.FirstOrDefault()?.Id;
        if (string.IsNullOrEmpty(groupId))
        {
            throw new EntryPointNotFoundException("No group available, need to create a group and upload a report");
        }

When I attempted to load the Workspace containing the reports in the Power BI portal, I found that I no longer had access, because for some reason my pro license was now a free license (I was also unable to publish reports to the portal). After renewing the license for me, I regained access and once again could publish.

My current assumption is that the two are related. I'm trying to find how Power BI access is granted from the website, and if it is possible that the account used to access this could have also been downgraded to free?!

Does anyone know how I can find which user has access to the report? Is it defined on the App Service in Azure? Unfortunately, everyone who knows about the website set up were either contractors or have left, so there is no one else here I can turn to.