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In the case of a custom field, you can use a group or multi-group select field.
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Groups are revealed at the time of Approval Path start
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Resolve user/users on
There are two options that allow you to reveal the group,
Approval start
Step start
If the “approval start” option is selected, the group will be revealed as soon as the the approval starts (in the event of the group missing from the issue field, this step will be skipped or definition will not be created).
Step start option, however, will only reveal the group once the path has reached to the step.
Once group or groups are determined this step behaves the same as Group Step.
Creator exclusion
Similar to group step, exclusion of creator as an approver from the group is possible by selecting this option.