Is it reasonable to send a message to the boss asking for leave as absenteeism?

According to the relevant provisions of China's "Labor Contract Law", if the laborer provides labor for the employer, the employer shall pay remuneration to the laborer according to the actual work situation. If you don't go through the relevant formalities, your behavior can be regarded as absenteeism. It's not the inevitable reason why you sent a text message asking for leave. You can ask someone else to ask your employer for leave on your behalf. But even if your behavior is deemed as absenteeism, the employer can't deduct three days' salary. You can complain to the local labor inspection brigade, or apply for labor arbitration for the employer to deduct wages.