CG Cloud on scratch org: can’t create External Client App, Connected App pairing fails

I have an Enterprise org and I created a scratch org from it to set up Consumer Goods Cloud.

Setup docs say “Create an External Client App”, but when I try that in the scratch org I get:

“The Org Scoped External Client App must be in the format DeveloperOrganizationId:ExternalClientAppDeveloperName”

So: are ECAs simply not supported in scratch orgs?

Since ECA didn’t work, I tried using a normal Connected App instead. I created the Connected App (OAuth enabled, cert uploaded)

And i go to Processing Services Pairing App → Add connection details. I entered the Connected App’s consumer key.

When click Connect I get:

“We couldn't create a tenant. Check the Consumer Key is valid and the Connected App configuration is correct..”

Questions:

• Is ECA creation in a scratch org unsupported?
• If yes, is a Connected App supposed to work with Processing Services Pairing App?
• If yes, why am I still getting the same error despite reviewing the entire configuration dozens of times?

Note: I know that the public certificate can expire, and I pay attention to this. Every time I try, if the certificate has expired, I download the new public key and upload it to the connected app.

My Connected App Configuration:

External Client Apps need to be sourced from long-lived environments.

Therefore, no you cannot create External Client Apps in Salesforce Scratch Orgs. You should also avoid new Connected Apps to the greatest extent possible. It's clear that Salesforce would like to find a way to deprecate those and they are already harder to deploy than they were a few months ago.

Create your ECA in your permanent org, either use it as a local or add it to your package (depending on your project and process), and manage it from the parent org.

Additional guidance on ECAs.