Realpage offers payments on their website and landlords typically pass on the service costs to their tenants in the form of a $5 “service fee” as itemized by Realpage. Compared to a $10 fee to get a cashier’s check to pay in person (because ACH is done by Realpage), you’re saving $5/mo. (Cash is generally not accepted because they don’t want to be storing cash on location.)
If there is no way to avoid a fee, they should just bake it into the rent price. They just look petty by charging it separately.
I’m also surprised by the need for a cashier’s check. I’ve needed those on occasion for a security deposit to move in, but monthly rent was also accepted with a simple personal check.