We’ve installed the NMI plugin to the WordPress app and connected it with FunnelKit. The NMI plugin uses Customer Vault to save customer details for future purchases (one-click upsells). However, there is an error, as every time a user tries to complete the checkout, this error occurs: “Gateway Error: Unable to add customer.”

We’ve installed the NMI plugin to the WordPress app and connected it with FunnelKit. The NMI plugin uses Customer Vault to save customer details for future purchases (one-click upsells). However, there is an error, as every time a user tries to complete the checkout, this error occurs: “Gateway Error: Unable to add customer.”