When merging contacts in Zendesk, be sure to merge into the contact created by Talkdesk. If you fail to do so, you may experience seemingly random failed ticket pops or ticket creation. Talkdesk uses Zendesk's contact ID to create a ticket for any contact. If a contact created by Talkdesk has been merged into another contact, it will be deleted, and Talkdesk will try to reference a Zendesk ID that no longer exists. Due to Zendesk's merge behavior, agents must merge into any contact that has been created by Talkdesk.
Here is an example of how to merge properly. Here, "Jonathan Sparks" is a contact with no phone number and is not associated with Talkdesk. Another contact was created when Jonathan called in on an unknown number. We must merge into that contact.
Email address in contacts merged in Zendesk
The primary email address of the contact created by Talkdesk may have been automatically generated, thus looking like this: email@example.com
If you merge a contact that contains a real email address into a Talkdesk contact (the receiving user), that real email address will be added as secondary and the email address generated by Talkdesk will be kept as primary.
To avoid issues with undelivered emails when reaching out to the contact by email, you should edit the email addresses so that the Primary email is the real address, and the (secondary) Email is the one generated by Talkdesk, i.e., firstname.lastname@example.org
For more information, please check Zendesk's documentation on merging duplicate accounts.