In the module description, UC Sage Payments Gateway used to advertise support for recurring fees through UC Recurring Payments and Subscriptions. If it ever worked, I don't think it's working now.

UC Recurring Payments and Subscriptions is currently in 'alpha' release. What needs to be done to get recurring fees support implemented for UC Sage Payments Gateway? Should we use the UC Recurring Payments and Subscriptions module or code it directly into the UC Sage Payments Gateway module?

As a workaround, you can use your Sage Virtual Terminal to change payments to a recurring type.