This article provides the steps to retrieve the ID of a Resolution on Jira Cloud.
Here, we’re retrieving the ID of the “Declined” Resolution.
Log in as a Jira admin in your cloud instance.
Click on the admin icon(cog wheel) at the top right and click on “Issues”.
Click on “Resolutions” under “ISSUE ATTRIBUTES” in the left panel.
Click “Edit” next to the desired resolution (here, “Declined”)
The ID of this resolution is the number after "?id=" at the end of the URL.