It's only a retaining fee, you see.

这只是一笔预约费啊，知道吗。

youdao

Retained Firefighters are paid a monthly retaining fee, plus drill night attendance, emergency call out fees, as well as annual holiday leave.

BBC: NI fire service recruiting part-time firefighters

"After listening to feedback from our existing customers, a small number of whom do not feel their businesses would benefit from these changes, we will be retaining the fee-free option for existing customers, " a spokesman said.

BBC: Santander U-turn on free business accounts