Azure Monitor datasource error: "issue communicating with your datasource"

I’m trying to connect a trial GrafanaCloud install to an Azure Monitor data source, and have configured as per the Grafana docs with the one difference that the Default subscription Id is shown on that page as a simple text control, where I’m seeing it as a dropdown list with no selection options.

Suspect the absence of options is due to the error I’m getting when I use the Save & Test button: a big red box appears above the button showing the text

  1. Successfully queried the Application Insights service. 2. Azure Log Analytics:

followed by some html that, when saved & viewed separately, is a little error page with the Grafana logo & the message

Grafana datasource error
There was an issue communicating with your datasource.
If you see this message for more than a few moments, please email support @ grafana . com

I’ve seen the similar topic that appeared to be resolved by modifying access through Azure CLI but - with little expectation, since it’s now in the documentation linked above as an alternative for step 4 - I’ve tried that to no avail.

Anyone seen similar behaviour and care to make a suggestion please?