Can you delete the connection and then add a new connection?
You can see all the connections for the flow on the details screen:
Can you also try deleting the send mail action and then re-adding it
The connections in use by Apps and Flows can also be found here:
Choose a connection, then click ... , then select Details:
Click Flows using this connection are then listed:
If the connection is working for other flows and apps, then the issue is likely to be with the current flow.
However, it is usually far quicker to delete the action and re-create it, or start again and create a new flow if it's a short flow, or to use a new copy of the flow using Save As than trying to figure out what's gone wrong.
Ellis
