Use a shared mailbox on a mobile device (phone or tablet)

[NodorinaMing]

Hi,
I am using Andriod Samsung mobile phone.
I have full permission with send as permission to a shared mailbox. Both mailboxes hosted on line.
Reading https://support.office.com/en-us/article/open-and-use-a-shared-mailbox-in-outlook-d94a8e9e-21f1-4240...

Accessing shared mailbox from mobile phone is supported.

However, this is not working
Error
Authenticated Failed
That did not work. You may not have the right permission to add this mailbox or this mailbox does't exist.

What could be the issue? 

TQ

[#2]

Just in case, verify via the desktop client or OWA whether permissions are working as expected. If everything is OK there, open a support case via the in-app experience on Outlook mobile.