Tested using Elastic / Kibana Version 8.11.1 docker containers.
The Kibana 8 connector / rule APIs documentation notes that the field actionTypeId has been updated to connector_type_id.
This field is accepted when you create an action via API but the response payload still uses actionTypeId:
Request:
{"connector_type_id":".index","name":"<site name> Alert Index","config":{"index":"alerts-<site id>","refresh":false,"executionTimeField":"@timestamp"}}
Response:
[{"id":"35fd9e50-92ba-11ee-b15e-af8b4f215882","actionTypeId":".index","name":"Test Name Alert Index","isMissingSecrets":false,"config":{"index":"alerts-test","refresh":false,"executionTimeField":"@timestamp"},"isPreconfigured":false,"isDeprecated":false,"isSystemAction":false,"referencedByCount":0}]
If you then try and create a rule using this connector it fails to recognize the field at all with the response:
{"statusCode":400,"error":"Bad Request","message":"[request body.actions.0.connector_type_id]: definition for this key is missing"}
Using actionTypeId in the connector creation request works.