Go to: https://myaccount.google.com/permissions
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From there, scroll or search for "Repunzel" and click on the entry:
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Scroll to the bottom and click on "Delete all connections you have with Repunzel". Click "Confirm".
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Then go back to app.repunzel.com, log out and then login again. It will ask you if Repunzel can send email through your Gmail account. Click Allow to all the prompts.
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Send yourself a test email to make sure it works and then try sending your submission emails again.