In ShipEngine, you have two types of payment methods:
Your ShipEngine Balance payment method, which funds the balance that pays for your ShipEngine Carrier labels, package insurance fees, and any post-shipment adjustments that may occur for those labels.
Your subscription payment method, which pays for your monthly subscription fee and any API overage fees you may incur each month.
If you are on the Free plan, you will not have a payment method to manage for your subscription.
To edit or change your payment methods: