Assuming the tire fills and seats but has a leak, (copied from online)
- Double check the rim tape seal. Re-tape, or add a second layer of rim tape. The telling sign of a rim tape leak is air escaping from the valve stem hole. A leak at the valve stem hole does not necessarily mean the problem is at the valve. It means that air is entering the rim cavity through a spoke hole (rim tape leak) and then escaping through the path of least resistance (the valve stem hole).
- Add more sealant and ride. If the tire inflates and seats but small leaks around the tire bead keep it from staying inflated, try adding more sealant and take a short 15-20 minute ride to keep the sealant circulating to stop the leak.