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With Perform As User, you can specify a different user account that owns the necessary permissions. Usually, this user account is assumed to be only technical (impersonation), with broad permissions, but not used to log into a Jira account as a person. If you don't specify
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a user here, the transition on the related
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issue is performed
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as the same user
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who triggered this post function on the origin issue by default.
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Therefore that user must have the necessary permissions on the related issue.
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In some restrictive
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setups, that user might not
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have the permissions on the related issue
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or even might not
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have access to the project of the related issue
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.
In combination with the 'User is in Any Users' Condition, you can hide a transition from all other users than the 'Perform As User' user.