SharePoint Admin - Why can't I add new allowed domains to "More external sharing settings"?

Question

I have a list of IP addresses and domains listed on this settings page, to which now all of a sudden I can't add more. There are only 31 separate domains here, separated by carriage return. Am I doing something wrong or have I found a bug?

According to https://docs.microsoft.com/en-us/sharepoint/restricted-domains-sharing, "To limit domains at the organization level

1. Go to the Sharing page of the SharePoint admin center, and sign in with an account that has admin permissions for your organization. Note If you have Office 365 Germany, sign in to the Microsoft 365 admin center, then browse to the SharePoint admin center and open the Sharing page. If you have Office 365 operated by 21Vianet (China), sign in to the Microsoft 365 admin center, then browse to the SharePoint admin center and open the Sharing page.
2. Under Advanced settings for external sharing, select the Limit external sharing by domain check box, and then select Add domains.
3. To create an allow list (most restrictive), select Allow only specific domains; to block only the domains you specify, select Block specific domains.
4. List the domains (maximum of 3000) in the box provided, using the format domain.com. If listing more than one domain, enter each domain on a new line. Note Wildcards are not supported for domain entries.
5. Select Save.

The steps above deserve to be updated since some recent UI changes by Microsoft. For step 2, it should state "On the left navigation pane, select Policies | Sharing and then on the main page, under the External Sharing heading, click 'More external sharing', then click the button 'Add domains'"

Regardless, clicking the Save button on the flyout menu (where you enter the domains) doesn't save anything! The Save button back on the main page doesn't save the domains either! If you go away and come back to this page, you'll find that your changes weren't saved. It does appear to be a Microsoft bug (we're reporting it) but maybe it's something else--like perhaps the domains list won't save if one of the domains is somehow invalid. If you have any other ideas to help me advance, please let me know.

Answer 1

Check the values with (Get-SPOTenant).SharingAllowedDomainList. I verified I was able to add 2999 domains via the SPO Admin Center and got back 2999 domains via the PoSh cmdlet.

You can also add it via Set-SPOTenant -SharingAllowedDomainList as noted in the article you referenced. This may be a better option.

If the format of one or domains was invalid, when you attempted to save on the Sharing page, you would get back the error:

Formatting of this domain name is not valid.

But, given you can't set the domains via Set-SPOTenant, you will need to work directly with Microsoft on a fix.

Answer 2

Microsoft has confirmed that this issue was due to a problem they've now resolved on their back end.

Answer 3

i had the same issue and was stupid, after you add the domain , and hit save, scroll down the page and hit the save button there, boom\