Shared Mailboxes are not working for Approval actions in Flow currently.
Please make the change so Shared Mailboxes are supported in Microsoft Flow Approvals Centre
I am also unable to utilize the approval function when I've entered a shared mailbox as the 'approver' in MS Flow.
The only work arround I can think of is to manually add every member of the mailbox as 'approver'. This way, when hitting the approve/reject button from the shared mailbox, the user will be directed to their personal flow environment.
The downsite of this is that the user will not automaticly be redirected the relevant request. It will open the main flow approval center and the user will have to manually look for the relevant request and approve/reject it.
I really do hope this feature is added as soon as possible. It is my experience that 'big' companies approve/reject on a department level, rather then on employee level. As most requests are directed to a department/shared mailbox. Anyway it would be nice to have both options available.