Error when embedding Power BI report in app: Operation returned an invalid status code 'Forbidden'

I am embedding a Power BI report in a Blazor web app. It was working fine until today, when it suddenly stopped working. Now, navigating to a page in the app which contains an embedded Power BI report results in the following error:

Error: Microsoft.Rest.HttpOperationException: Operation returned an invalid status code 'Forbidden'

The app uses a service principal to authenticate with the Power BI workspace.

Power BI license info:

// Retrieve the necessary info to embed a Power BI report in the app
public async Task<EmbeddedReportViewModel> GetReportEmbedding(string workspaceId, string reportId)
{
var tenantId = _configuration["AzureAd:TenantId"];
var clientId = _configuration["AzureAd:ClientId"];
var clientSecret = _configuration["AzureAd:ClientSecret"];
var authorityUri = new Uri($"https://login.microsoftonline.com/{tenantId}");

var app = ConfidentialClientApplicationBuilder
.Create(clientId)
.WithClientSecret(clientSecret)
.WithAuthority(authorityUri)
.Build();

var powerbiApiDefaultScope = "https://analysis.windows.net/powerbi/api/.default";
var scopes = new string[] { powerbiApiDefaultScope };

var authResult = await app.AcquireTokenForClient(scopes).ExecuteAsync();

string accessToken = authResult.AccessToken;

// Create a Power BI client which will interact with Power BI's REST API
var tokenCredentials = new TokenCredentials(accessToken, "Bearer");
var urlPowerBiServiceApiRoot = "https://api.powerbi.com/";
var pbiClient = new PowerBIClient(new Uri(urlPowerBiServiceApiRoot), tokenCredentials);

// Fetch meta data for the desired Power BI report
var workspaceIdGuid = new Guid(workspaceId);
var reportIdGuid = new Guid(reportId);
var report = pbiClient.Reports.GetReportInGroup(workspaceIdGuid, reportIdGuid);

// Generate embed token which grants permission to view the report
var tokenRequest = new GenerateTokenRequest(TokenAccessLevel.View, report.DatasetId);
var embedTokenResponse = await pbiClient.Reports.GenerateTokenAsync(workspaceIdGuid, reportIdGuid, tokenRequest);

var reportViewModel = new EmbeddedReportViewModel(
report.Id.ToString(),
report.Name,
report.EmbedUrl,
embedTokenResponse.Token
);

return reportViewModel;
}
​

Any help is very appreciated!