I have relatives in Shenzhen and Zhuhai, and I visit Hong Kong about twice or three times a year. It's convenient to do so while I'm there.
Actually, paying in cash would also be fine; there's a China Bank ATM downstairs. After inserting your mainland bank card and withdrawing the money, you can go upstairs to pay.
It's not that I didn't personally pay and realize there was a problem with the information; I also had to reprint the physical ID again (OFCA thought the previous photo wasn't good...?); the screenshot of my Guangxi license was large enough, but they still found it blurry, so I sent the original copy; and the documents submitted through GovHK mysteriously disappeared before payment, so I immediately emailed them the original photos.