At the Worldwide Developers Conference in 2017, Apple informed developers that macOS High Sierra would be the last version of macOS to run 32-bit apps. Apple is now notifying customers when they are using a 32-bit app with a one-time alert that appears when a 32-bit app is launched.
Billings Pro is a 32-bit application and even with this message, you can continue to use Billings Pro on macOS High Sierra with no adverse effects on your data or your computer. Marketcircle will release a 64-bit version of Billings Pro before the launch of Apple's latest OS.
Self-Serve Customers: There are no plans to update Billings Pro Server Admin to 64-bit. We do not recommend updating the computer with Billings Pro Server Admin installed to future versions of macOS. For more more information check out Announcing Our Goodbye To Self-Serve.