:-( Something went wrong with OWA. Yes, yes it did... and this is how I fixed it.
Updated: Dec 9, 2020
I've been setting up Office 365 tenant for years now. I was asked by a friend to take a look at a new Office 365 tenant that just wouldn't load outlook. I thought it would be a quick and easy fix but this one was a new one for me.
When she tried to open Outlook Web App (OWA) she was getting the dreaded error.
":-( Something went wrong"
There were also MS Exchange errors when creating new users. Even though an Office 365 E5 license was selected.
"You can't assign licenses that contain these conflicting services: Exchange Online (Plan 1), Exchange Online (Plan 2). Review the services included with each license and try again."
(Exchange Online Plan 2 is included with Office 365 E5, a Plan 1 license option wasn't available on the tenant and was not selected for the user.)
After checking out the account I saw that even though the Office 365 E5 license was assigned days earlier the mailbox was still stuck at "We are preparing a mailbox for this user."
I tried to open the Exchange Admin center and received a 500 error. So no dice... I was able to connect to exchange with PowerShell but of course, there were no mailboxes to manage.
The tenant had been configured with a custom domain, I checked the Domain status page in the Admin Center.
To open the Domains page:
On the Office Portal select Admin
It was as though the tenant had been provisioned without Exchange. As a shot in the dark, I changed the domain for my user name from the custom domain to the initial domain (tenantname.onmicrosoft.com). Poof! I had a mailbox, could get into OWA and could manage Exchange. I changed the user name fo another user account and the mailbox was created.
Then I tried to swap the domain back to the custom domain. I received an error that the custom domain was not configured yet. The custom domain for this site was purchased from Office 365 and it was as if the DNS records needed to be reset. I decided to change the default domain back to the initial domain (tenantname.onmicrosoft.com).
To do this using the Admin Center you can't use the new admin center GUI.
Turn off the new experience using the toggle on the top right of the Admin Center.
On the classic Domains page there the option to change the default domain is now available when a domain is selected.
You can also change the default domain through PowerShell using the Set-MsolDomain cmdlet.
Set-MsolDomain -Name "tenantname.onmicrosoft.com" -IsDefault
I changed back default domain back to the initial domain, waited about 30 min then tried to change the domain on my user account back to the custom domain. No errors this time! I changed the default domain for the tenant back to the custom domain and swapped the second account username back to the custom domain, no errors this time either. To make sure everything is now working correctly, I created a new test user, assigned an E5 license, no errors and the mailbox was created.
What I believe happened is that the new tenant was created and the custom domain was set up so quickly exchange didn't have a chance to provision with the initial domain (tenantname.onmicrosoft.com). Setting a user with the initial domain and assigning it a license forced the mailbox/exchange creation and swapping the default domains for the tenant reset the DNS.