TLDR: Check your cron job errors for missing tables and columns that should have been added.
My solution ended up being related to the extension not fully installing itself. I was missing three tables in my database, which I was able to add with the help of Ebizmarts support and some of my own tinkering in the database.
AOE Scheduler was a HUGE help to see the missing tables that the cron jobs were referring to - you could always get this information from the
/var/logs folder as well.
Once these tables were present and the cron jobs came back with no errors, webhooks were automatically created in my Mailchimp account without any extra effort from myself.
Specifically, the following tables were missing from my installation:
Additionally, a column named "mailchimp_campaign_id" was missing from my "sales_flat_order" table. I manually added this table based on it's PHP setup file with
VARCHAR(16) Default NULL settings.
All information to create these tables can be found in the
app/code/community/Ebizmarts/MailChimp/sql/mailchimp_setup folder from the extension installation package.
I received an
.sql file from MailChimp support to get the first two tables in my database, then had to run extension installation on my staging environment (not local host - MC support said there are issues with this for the webhooks) to generate the
mailchimp_errors table which was empty and I was able to export from that SQL db to my production version.
Mailchimp Support stated that the best way to install their extension was to place the site in maintenance mode & whitelist my IP, disable all caches, flush cache (not storage), logout of admin, add files via FTP, run permissions updates via SSH, flush cache, login to admin, enable caches, flush cache again, remove maitenance.flag, and wait for cronjobs to run and read errors if there were any.