To use the Tasker AI Generator feature, you need a Google Cloud API Key enabled for the Generative Language API.
To use this action, you'll have to get a Google AI Studio API Key on your Google account.
If you already have a Google API Key in Tasker, you can continue using it, but you have to enable the Generative Language API on your Google Cloud project here so you can continue to use it with both this, Say Wavenet and any other Google API that requires a key in Tasker.