So you've created a POPin, but you're hearing from your team that they cannot get in? Here are a few things to check:
You've created your POPin using the correct access option.
You did not add a distribution list (ex: firstname.lastname@example.org) to a POPin created with the 'Private' access option. While distribution lists themselves are not supported, you may invite everyone from your distribution list using your email browser to copy/paste the individuals from that list into the POPin invite box.
You've double checked you have all the right email address. If your company has multiple email addresses or domains for each employee, be sure you're inviting the one people know to use; otherwise invite them all, or communicate with your team which version of their email address you've authorized.
You've set the POPin to open at the right time. Is your POPin set to open in the future? Has it already closed? Adjust the start/end time if need be.