I created flow with a Post adaptive card in a chat or channel step. I am able to post the adaptive card to the intended Teams channel as long as I leave the Card Type ID field blank.
Post an adaptive card flows, without and with, respectively, Card Type ID.

If I include text in the Card Type ID field, I get the following error:
{
"error": {
"code": 400,
"message": "Environment id is null or empty",
"source": "flow-apim-msmanaged-na-westus-01.azure-apim.net",
"path": "choose[12]\\when[1]\\choose\\when[1]",
"policyId": "",
"clientRequestId": "XXXXXXXXXXXXXXXXXXXXXXXXXXXXXXX"
}
}
When someone responds flow config:
Based on YouTube videos I have watched, the fields should contain arbitrary matching strings so that the system will connect them. This feels like a bug on the Microsoft side to me... Any ideas?