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First, you need to enter a field by which you’d like to perform a search.
Start typing the field name into the upper input (number 1 on the screenshot).
When you start typing a key, a helper-list with autocompletion will appear. The field is based on the JSON path to the needed property. For example, if you need to search by the project key field – enter "fields.project.key" (you can build the actual path either by checking JSON view of your issue from the REST API response, or by checking a sample issue – Show Sample button).
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After then, enter the needed value in the criteria field (number 2 on the first screenshot).
If you need to search for multiple project keys – you have to switch the "=" to the "in". Then click on the appeared "+" button to add more keys.
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