Unfortunately, at this time, RoboKiller will not be able to support both lines on your Dual SIM device simultaneously. A RoboKiller subscription can only be linked to one of the two lines, most likely the main line. The secondary line will need to have its own subscription. Even with a second subscription, RoboKiller will not work as expected on both lines.
We are always looking to improve our app and make it accessible to all users on different devices. We hope to support both lines on Dual SIM devices seamlessly in the near future.