p12 api key for appointments plugin

@adminI am following the Appointments+ Google API instructions (which, of note, appear outdated) and cannot find a p12 download ability. that is, i found where to generate an OAuth 2.0 key and have the secret key, but the only download option Google is giving me is JSON - which I have. When I uploaded that version, however, and used that file name, the Appointments+ plugin gives me no love when I hit the test button.

I suppose some questions, then, may be:
Q: Is a JSON file supported by Appointments+?
Q: How can I convert JSON to p12?

I understand the latter is not a WPMUDEV issue, but still, seems like a relevant question.

Thank you!