They can make their own payment:

https://www.irs.gov/payments/direct-pay

Depending on the client and how tech savvy or not they are, I go to IRS DirectPay and schedule payments for clients from time to time...I can whip through it in less than 5 minutes, easier than having them get stuck and call me to help over the phone.

I give my clients the payment voucher, the 1040V,  and let them take care of it themselves. Why would I want to take on additional responsibility and get involved with electronically wiring the money. That is not my job. 

I did tell my client to go to the irs website for direct pay and it shows that I efiled the taxes but does not show an amount due!! I have never used that option before so I was not sure how to advise them