Hi ​@shand125, welcome to the Box Community!

The error you're encountering may be caused by External Collaboration Restrictions. Either your enterprise or the external users' organization may have policies in place restricting external collaborators to certain allowlisted domains only. If your domain or user account isn't on that allowlist, invitations to collaborate cannot be sent or accepted.

To learn more, see Limit collaboration to allowlisted domains.

Note

The limit on collaboration to allowlisted email domains goes both directions: Your user cannot invite someone who is not from one of the specified email domains, and someone not on the specific email domain cannot invite your user to collaborate.

To resolve, please confirm with your IT or Box admin that your user account and domain are included in the external collaboration allowlist. Also, please advise the users to check their External Collaboration setting and ensure that your domain is allowed on their side as well.

We also have a related community topic on access to shared documents and collaboration restrictions for more details:

If you have any other concerns, please do not hesitate to reach out to us. 

thank you. i am allowed on my end and will check with the other external 

Much appreciated—thanks for the quick confirmation that it’s allowed on your end!

Once you’ve checked with the external users and their admin has reviewed the collaboration settings, please try sending the invite again.

Let us know how it goes!