Hi @Holly Kosec ,
How did you invite these external users to a SharePoint site?
You could try to invite these external users in Azure Active Directory admin center.
Azure Active Directory admin center > Users > New guest user > Invite user > type Email address
Then these users will get Invitations emails. They have to click "Accept Invitation" in that email.
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Sorry for the delay, I am waiting to hear from the external user on whether that worked or not. I will reply ASAP!
Hi @Holly Kosec ,
Thanks for your reply. Comment here if you still need any help.