I just found the following under another post and it will work for my needs.  I called the number on the IRS website and was able to CANCEL the April 15th payment of my Taxpayer.  I will now send my Taxpayer a payment voucher and set up 'delayed' email reminders as July 15th nears.  Ultimately it will be up to the Taxpayer to make sure the payment(s) are made.

Here's the post I found:
  Can I cancel an Auto Debit payment:
  Yes, by calling the various agencies.
  https://www.irs.gov/payments/pay-taxes-by-electronic-funds-withdrawal#errors
  You can google YOUR state all by yourself.
  And you'll have to make sure the payments get made some other way...