In plain English, Viasat requires that they be the initiator (ACH Debit) in your contract unless you live in a state that requires other methods or unless Viasat grants some form of papal dispensation (click on the image to enlarge):
It's simply a preauthorization for Viasat to initiate the transfer. But yeah, other than current corporate policy there's no need to not allow the other way around other than to ensure payment for service in advance (they don't trust you and probably for good reason looking at some of the wild posts that show up here). Initiating an ACH Credit transaction without Viasat's authorization, however, will most likely wind up with your access being cutoff when it fails to credit properly and someone says what the heck is this?
Regardless, use a credit card if possible - you'll find it easier to dispute erroneous charges and not be dinged until the dispute is resolved.
Disclaimer: I don't know what I'm taking about nor do I work for (or have Iever worked for) anyone who does ;)
The option Viasat and most others prefer is the same as swiping your credit/debit card at the grocery store or gas station where authorization and payment is immediate. When I get my bill in email, my account has already been charged, here is a copy/paste from last months bill ...
We've generated an invoice for your account today. Your payment method on file was charged yesterday, July 12th, 2018.
This makes it extremely difficult to dispute, and impossible to withhold payment. Pretty smart business practice when so many customers are displeased with your service that does not meet claims or expectations. And if you dispute the charges, GOOD LUCK getting a refund. YES, they will eventually "credit your account," but it is a painstaking process usually involving multiple phone calls and speaking to several people, which ultimately is a not so viable solution when you are on a limited fixed income and that "extra" money they took was earmarked for something else.
It is a convenient and reliable system that has benefits for both HONEST parties, however I feel the government needs to step in and regulate it. I feel the consumers "pre-authorization" to charge said account should be legally bound to a "pre-authorized" amount! I dont agree that my consent to charge my account should give them free reign to take what they want.