If you book online then you need to present your online reservation at the bus station ticket counter to exchange it for an actual bus ticket. All quick and very easy.

Sorya bus are not usually this late and slow. This particular bus driver (Phnom Penh to Kratie on 8 May at 9:45 am) was extremely cranky, extremely slow, and did not give us enough time to eat a meal on the ride for more than 8 hours.