Share Google Drive Folder via Zapier with Mailchim

问题:

I can't figure out how to format the "Custom Value for Sharing Preference" on this Zap I'm trying to create that will share a Google Drive folder with my new Mailchimp subscribers.

I've been able to get the File ID using the Drive API, but I'm not sure how to provide the Custom Value that should come from the New Mailchimp Subscriber Email.

If I simply choose the Email address from the Mailchimp dropdown provided by Zapier and test it, I get an error:

We had trouble sending your test through. The app returned "The permission type field is required.". This usually happens when your Zap is missing a required field or a field value isn't in a recognized format.

EDIT: Success via the Google Drive API test.

Using the sandbox available here, I know that I need to:

POST https://www.googleapis.com/drive/v3/files/fileId/permissions

the following Request Body

{
  "role": "reader",
  "type": "user",
  "emailAddress": "[e-mail]"
}

I've been able to run that test a few times with Google's sandbox, so I know I can do it. I just don't know how to pull this into Zapier.