請問點樣email追問client

I suggest you write an email as follows:

Hi (or Dear XX),

I have got your money ($XXX) but could you tell me what is it for?

You can either drop me an email or call me at (telephone number).

Regards,
(Your Name here)
(Position, Company Name)

Dear Mr/Ms xxxx,

I have received a payment from you on (date), but due to lack of data, I am not able to process your inquiry.
Please kindly contact me, either by phone or email, at your earliest convienient.

Thanks for your cooperation.