from field NOT displaying shared mailbox's email

I've created a support email under shared mailboxes and added some members. Then I added the shared mailbox to those members web app 365 outlook.

When I make a new email or reply to an email, the from field does not show my support email. I can not select the shared mailbox email. I waited over night too for it to set up.

Please let me know if anyone else has experienced this and what the solution was?

Thank you!
Patricia Rust