The Hikers Underground app helps you find shuttle providers and pay the shuttle provider with a credit card in the app.
The AT has a large informal network of shuttle providers. All of them are individually operated businesses. They set their own hours and often are only known by word of mouth or various lists.
This makes arranging a shuttle difficult sometimes. The Hikers Underground app helps make it easier.
Tips on AT Shuttles
Plan Ahead - You will have better results if you schedule your shuttles in advance. Especially during the busy season various parts of the trail may be difficult to find rides.
Stay in Contact - confirm with your driver the day of your scheduled shuttle.
Check Your Vehicle - if leaving a vehicle make sure anything of value is out of sight. Remember your wallet, keys and phone!
Info on parking, vandalism reports etc. Appalachian Trail Conservancy