Hi @Alfredo_Delgado
I write here the same message as in pymc-marketing github
My problem is the same but I am sure that it is not the answer 
if there will be not point to spend more then if I increase the hole budget, the budget allocation should not increase. In fact - it does.
Second thing - example notebook suggest it should allocate hole budget as the next step is limiting the budget based on saturation curves to show that it almost doesn’t affect outcome.
Finally and the most important, in library code it is impossible to not allocate hole budget, from budget_allocation.py
constraints = {"type": "eq", "fun": lambda x: np.sum(x) - total_budget}
that means that default constraints ensure us that budget will be sum up to 1. So somewhere in between something is going on badly.