Active demand (AD) represents a demand response scenario in which households and small commercial consumers participate in the grid management through appropriate modifications of their consumption patterns during certain time periods in return of a monetary reward. The participation is mediated by a new player, called aggregator, who gathers the flexibilities provided by its pool of subscribers to build up AD products. These are offered to energy system participants through various markets. After market closure, the role of the distribution system operator is to perform technical validation of AD products by checking their compatibility with network constraints and operation. Computational methods for accomplishing this task are described in this paper. First, technical validation is formulated as an optimal power flow (OPF) problem with the objective to minimize the curtailment of the AD products. Then, specific cases allowing for an exact solution of the OPF problem through bisection are described. Recently proposed convex relaxations can be exploited to tackle the OPF problem in general cases