So, there's a fair bit to get through here.
By default, the Systems Manager app, which provides jailbreak detection, location and the ability for users to chose from a list of apps, is installed. Now, if you don't have VPP set up (more of which here: https://documentation.meraki.com/SM/Apps_and_Software/Apple_Volume_Purchase_Program_(VPP) ) then the device will request an iTunes account
To avoid this, there's three things you can do
1. Change the Targets of the systems manager app in the dashboard to No Devices
2. Ensure that VPP is set up
3. Go to the systems manager app in dashboard and set, under Licenses, Purchase method to VPP device assignment: