Libra is an algorithm developed by the University of Zaragoza (UNIZAR) for the software company Alerce, optimizing the delivery process of Senda, its leading application for last-mile route optimization in the courier sector. The geocoding in Senda already used proprietary algorithms along with support from external GIS systems and tools for route assignment, optimization, and real-time monitoring. Now, with the new algorithm implemented in Senda, the problem of reallocating customers between delivery zones to balance the number of customers assigned to each zone is solved in just a few seconds. This balances the workload, minimizes delivery errors, and reduces costs. This algorithm, developed by the Numerical Analysis, Optimization, and Applications research group from the IUMA at UNIZAR, won the second ALIO Award for Excellence in the Practice of Operations Research, granted by the Latin-Iberian Operations Research Association.