I am researching the square-connect api, and am able to send out curl calls and receive responses without issue. My question is, can a sale on the iOS APP send a call to my MySQL database to keep the inventory up-to-date on both my iPad and my database or do I need to run a cron every 5min or so to pull data?
The Square Connect API does not currently provide notifications for events such as changes in inventory counts. I've passed this use case along to the Connect API engineering team.
Your suggested solution of periodically pulling inventory information is the recommended method at this time.