Adding Constraint to Solver

Hi,

I'm trying to add a constraint in Solver for a supply and demand problem, but Solver keeps coming back with 'unable to find a feasible solution.
The constraint needed to be added is B12:AH12 <= 4. Number of max days an order can be in transit for.

I've tried adding excess amount to the supply cells AJ13:15, but still Solver is unable to solve.

Your help is much appreciated.