Appt not showing on provider cal

I am having an issue where App+ only puts the appointment on the "General" calendar and not on the "service provider" calendar on gcal.

I am also getting a few repeat errors under the "logs" tab.

Error calling POST (400) Invalid attendee email.

Error calling PUT (404) Not Found

(I changed the domain and truncated the urls in this post)

A little more background: It worked fine until a few weeks ago. I didn't change anything prior to it not working. Each provider still has their same gcal keys etc. Using 2012 theme (no mods), and appt+ version 1.3.1.

Any help would be appreciated. This is an annoying glitch.