First of all, thanks for taking the time to read through our issue.
So, we have a Dialogflow project connected to an already existing google project. When we try to test our skills on google by the Integrations tab, it displays an error 'Precondition check failed' without any more information, even though it still updates and uses our Dialogflow intents as it should.
The problem comes when we update anything on the actions console or try to make an alpha deploy of our skill. The moment we change anything, it comes back to the default configuration with the message 'Start building your action by defining the main invocation.' on the main invocation.
We have no clue how to handle this problem or if we have to configure something special on either of the systems to make it work. Any ideas are welcome.
If you want to integrate the Google Assistant with Dialoflow, I strongly recommend you check the new development Google Assistant's platform with a built-in conversation builder, here. Furthermore, there is a quick start guide and conversational actions guide.
As I mentioned in the first comment, you need to have appropriate permissions to create an interaction within Dialogflow, you can check the pre-defined roles here. In addition, since you are starting with Dialogflow, I would advise you to start with the available quick-starts and the setup tutorial, which explains how to begin using Dialogflow.