Hello @kristie,
My name is Henry and I am happy to assist with your inquiry, and appreciate you contacting LastPass Support!
I am sorry about the issues you are having with your colleague's account. Are they receiving an activation code on the invite? If they are not receiving the code, it is possible they already had an existing lastpass account on the same email. In this case, they will need to either delete or reset the account on this link. Once reset or deleted, please try to add them again.
Please let me know if this worked or if further assistance is required.
Thank you,
Henry | Customer Care
They have never used Last Pass before.
Please have them reset their lastpass account. After that, ask them to accept the invite. If the issue persists, please contact our support team as we will need to check on the specific users.