Hi everyone.
We encountered this issue.
In the Bigcommerce, If a Customer uses a Credit Card during the checkout process, we have to Override their "Default Payment" method on the sales order. It needs to be overwritten with "AUTH NET." I just conducted a test transaction. The Customer in question has a default payment method of "ACH." But, during the checkout process I used a Credit Card. When the order synced to Acumatica, the Sales Order pulled the default payment method of "ACH." This issue gets even worse when a Customer has a Default Payment Method of "CREDITCARD" in our system. In that scenario a Customer could pay with a credit card during Checkout and then Acumatica will run their card again when the order is invoiced. Double charging the Customer.
