Detail Problem:
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When user sends several invitations, only the latest one is valid and can be used to register. We would like that the user can click on whatever link received and that it still works. This means not doing an new invite, just sending a notification again on the same invitation id.
Reproduction steps:
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Do an invitation, click on re-send the invite several times. The user receives as many notifications, with different invitation ids.
https://www.dropbox.com/s/wehwy57h5x3ed4d/Screenshot%202018-07-19%2019.34.16.png?dl=0
