The Unknown status indicates that the result of a payment attempt is unclear, and Fusebill will pause billing on this customer until it is clarified by a user interaction. It is to indicate that the system is unsure of how the payment ultimately resolved within the gateway after the request was made. This could be due to not receiving a response from the gateway (such as a response timeout) or the response received from the gateway wasn't a clear success or failure.
The status and hold prevents duplication of any collections from a customer and avoids potential billing problems. It does this by pausing billing automation on the customer and preventing any other actions on that customer until it the unknown payment is resolved. Once resolved, billing will resume, and Fusebill will catch up, one bill at a time.
From within Fusebill, or through the API, a user in your account will need to manually resolve the payment as either successful or failed. If you go to the payments tab on the customer, you will see a payment with a status of 'Unknown'. If you click into the details of that unknown payment, you will have the option of manually marking it as successful or failed. If you log into your gateway and find this payment, you will be able to see if it was successful or failed. If you are not able to find the payment at all, that likely means the gateway never received it and you should mark it as failed.