When you're sharing a survey with a user who's in the same Qualtrics license as you, and you find them in the address book by name, you _don't_ have to worry about this button. The survey will just go to your colleague's account automatically.
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However, there are other circumstances where we aren't sure of the identity of the recipient, and want to add an extra layer of security. In these cases, you will share with your collaborator's email address. This collaborator will then receive a code that they must enter into the Accept Collaboration window for the survey to appear on their account.
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There are three circumstances where a user is going to receive a code to collaborate:
1. The user you invited to collaborate is from outside of your organization or Qualtrics license. (Remember: some organizations may have more than one license with Qualtrics. For example, a university’s Psychology department and its Registrar may have purchased their own brands.)
2. The user you invited to collaborate _only just_ created their Qualtrics account.
3. The user you invited to collaborate is in your organization, but you didn’t click their name to select them from the address book. Instead, you typed in their email address and submitted the change before selecting the specific account.
This update acts as both as a vital security update and as a major improvement on sharing with people who have multiple accounts. Previously, you had to share with an email address, then hope the user logged into the correct account, and sometimes the survey ended up in the wrong spot, so you had to remove it and try again... Now, you simply share with an email address, and the recipient of the survey simply puts the code into the account they want to access the survey from.
You can learn more about the details on the Collaboration page.
(PS - remember, if the person you want to share with doesn't pop up in the address book, share with the user's email address! Not the username! For example, I may have an account with SSO whose username is kate @ example.com#community, but you'd share with kate @ example.com.)