Thanks for asking question! Like the rest of the sample, recording start/stop only needs to the ACS connection string. But storing it in blobstore needs more setup.
As you have provided these connection strings. There's one more setup step and you need to create a webhook event subscription in the ACS resource:
This is needed so that your sample server can be notified by ACS when a new ACS recording becomes available.
Hope this helps, Let us know.