When NetSuite Support cases are synced with Zendesk Tickets, the associated NetSuite messages are also synced to Zendesk Comments.
Note: Attachments sync is not supported between Zendesk Tickets and NetSuite Support Cases.
If a NetSuite Case exists with messages before the integration app data flow was turned on, and this Case was synced to Zendesk along with messages, then the existing messages will not sync over to Zendesk. Only messages that are created after the flow is turned on will be synced.
This is not supported in the integration app by design because of the following limitations in Zendesk. Zendesk has rate limiting which only allows 15 comments to be added in a ticket within a 10 minute period. Refer to the Rate Limits section in Zendesk REST API page: https://support.zendesk.com/hc/en-us/articles/206522987-Zendesk-REST-API-basics#rate
If there are a lot of existing messages, they cannot be synced in real time or in batch without hitting the rate limit.
Note on private and public messages
In NetSuite, there are private and public messages. In Zendesk, they are called internal notes and comments respectively.
When messages are pushed from NetSuite to Zendesk, the private messages are synced to internal notes and the public messages are synced to comments. The reverse flow does not exhibit the same behavior.
When Zendesk comments are pushed to NetSuite, the internal notes and comments both sync to the public messages in NetSuite. You can set up the integrator to either sync internal notes or comments only or you can set up to sync both types of messages together.
Screens showing data flow from NetSuite to Zendesk
Message in NetSuite:
integrator.io Ticket Sync settings. Run the data flow.
Comment in Zendesk