We have an Office 365 Business Premium plan that I've been learning as I go along setting it up. I'm in the process of setting up SharePoint sites and folders to store our shared information by department to migrate it from our on-site NAS. I've created a private folder for our Tech department that I've placed some documents in and one of the documents I want to share with an external user to collaborate on.
I've tried the regular "Share" button on the document but the "Anyone" option is greyed out. I tried to specify to share with specific people but it just told me that sharing with people outside the organisation isn't permitted. I've gone through all the steps listed here, here, here, and here and everything looks to be set up fine, all the options say to allow external access if selected. Except I can't.
Is there something I'm missing? Is it because I set the whole site to be private? I would rather not have the site contents accessible by anyone other than the Tech dept. except the files I choose to share.