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In the new Jira Cloud instance, the project name and key should be the same as those you have in Jira Server.
Do not delete the existing Jira integration in Zephyr. Just edit the settings to point to the new Jira Cloud instance. Otherwise, all the mappings and links will be lost.
After connecting to the new Jira instance, you need to do one of the following to update the webhooks:
Update some data in your project.
Configure Jira synchronization for your release on the Requirements page by clicking and selecting Jira Sync Config from the context menu:
click Update Webhook to recreate the required webhooks: