On the Big Sandwich site copy the feed URL for the show you wish to add (it will look something like https://bigsandwich.co/feed/wplanet/). Then open Overcast to add a new podcast. Paste in the feed URL and select the option to use ‘Username’ and then enter your username and password.
If you are using an older version of Overcast which doesn’t have the Username option you will need to follow the instructions below.