What are the reasons for being unable to schedule Subject 4 on 12123?

[DiDaniel]

Here are the specific reasons why you can't schedule Subject 4: 1. Low priority: When there are too many people scheduling at the same time, your priority may be lower than others. There's no need to rush to log in for scheduling, as the allocation of slots is based on priority. Even if you schedule early, you may not succeed if your priority is lower than others. For first-time scheduling of Subject 1 exam, the sorting time is based on when the user initially applied for a motor vehicle driver's license. For non-first-time scheduling of subject exams, the sorting time is based on the date of the last exam. 2. System issues: Sometimes when the system is under excessive load, some students may not be able to schedule exams and can only wait for the system to be repaired.