When sending email from Microsoft Flow, I got the error below:
"You don’t have permissions to send emails on behalf of . Contact to check shared mailbox permissions and gain access."
Click "Send an email" action and get the detailed error message:
"You are not authorized to send mail on behalf of the specified sending account."
Some people suggests, For the Shared Mailbox, you just need to make sure that you or whoever/whatever account will execute the flow will have Send As permissions to it. Then just set the From parameter of the function to the email address of the shared mailbox
It may work. But the easier option is to leave "From (Send as)" field blank.