If I understand your request you would like to edit existing issues including those with custom fields. An example message to update assignee, priority and 2 custom fields for the issue QA-31 would be :
example input data
There are a lot of other great examples of JIRA REST API available from here:
I’m a designer on the Jira team. For a long time, I’ve fielded questions from other designers about how they should be using Jira Software with their design team. I’ve also heard feedback from other ...
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