ACH is the recommended payment method for customers since they do not incur a credit card convenience fee. To allow ACH payments you will need to enable ACH on Stripe.
When you receive an ACH payment, Stripe charges you (the supplier) 0.8% with a $5.00 cap. This will be displayed as "Stripe fees" in your dashboard.
To accept ACH bank transfers from customers on Lumi, visit this page and follow the instructions to enable this feature.
The button you need to click says "Enable ACH" as seen in the screenshot below. If you do not see this button it means you have already enabled the feature.