This feature is available on the following plans:
Growth
Premium
AppSumo*
Setting Up the Messaging
Head to Settings, then the Intro/Outro option on the left.

To apply your new Intro and/or Outro message, click Browse to open your file finder and find the MP3
Note: The Max File Size for Intro/Outro messaging is 10MBThen click the orange Upload button next to whichever one you've started and it will upload.
Applying the Intro & Outro Messaging
Upload your episode as normal and fill in Title, Description, etc.

As you scroll down, make sure the slider for Pre/Post-roll is turned on (Orange) and this will automatically apply your messaging you set up to this episode!
If you need to apply your Intro and/or Outro to any existing episodes, click the 3 dots next to the episode, then Edit. You'll now find the toggle to turn it on in there!
* Not included with AppSumo accounts but can be purchased as an add-on.