[EWS][ps][windows] Cannot access shared mailbox

So I have already added a shared mailbox but when I try to access it I get this message "Cannot display the folder. Microsoft Outlook cannot access the specified folder location. The operation failed. An object cannot be found."

Tried going through Powershell and would use this command "Add‐MSOnlineMailPermission ‐Identity (*****@email.com)‐TrustedUser (*****@email.com) ‐GrantFullAccess True ‐GrantSendAs True ‐Credential
$cred"

But it kept saying that addmsonlinemailpermission was not a cmd.

Not to sure what to do now.