If the customer has an Open Issue already
If the sender's phone number already has an open issue, the new message will be transferred into a Jira comment in the open issue.
If the customer doesn't have an Open Issues
A new Jira ticket will be created if the sender's number does not have an open issue.
If the customer has resolved tickets
If your agents set the previous customer tickets resolution same as that configured in WhatsApp Connector for Jira project settings, then a new ticket will be created
To learn how a Jira issue turns into a WhatsApp message, click on this link here.