Hey Peter!
These are all good questions, and to be honest, it is something that I would love to get some guides around…but alas, limited time 
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Luckily I use Grafana Cloud, so I know roughly where you are going wrong here 
. The Prometheus credentials that you are referring to are used when you are using Prometheus’s remote_write functionality. By default Prometheus will scrape metrics from your /metrics endpoint, but with Grafana cloud, that is not an option. Instead they want you to go down the route of pushing metrics via Grafana Agent (I have an issue for this in PromEx to make it easier for people Add support to bundle GrafanaAgent to push metrics · Issue #44 · akoutmos/prom_ex · GitHub, but I haven’t had a chance to wrap it up). How are you running your app? Is it easy for you to run Grafana Agent along side it?
In addition, you should be making an access token in Grafana (go to your instance’s /org/apikeys route to do so) and using the :auth_token value in PromEx so that PromEx can publish dashboards for you. The :host value should just be the url of your Grafana Cloud instance.
Hopefully that help
