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If you enter an empty plan a message will show up with the Add user button.
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Click the button and a modal will show up.
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If you enter a plan with users already present then there is another Add user button under the list of added users.
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You can also set up it here on the following page:
https://{YOUR_INSTANCE}.atlassian.net/secure/admin/GlobalPermissions!default.jspa
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Changing the order of users
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If you see the label just click Save Planand all changes will be saved. You will also be notified that the changes are not saved in a pop-up when you try to exit the page.
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