Adding Constraint to Solver

After half a day, I will venture to comment. I am confused by the constraint that B12:AH12 must be less than or equal to 4. B12:AH12 are hard coded references to the transit times entered in AO:AQ and, as far as I can tell, cannot change. There is nothing in the spreadsheet or Solver model that allows the transit time for Customer1 from Perth (D12 which is mirroring AQ13) to be anything but 7. There is nothing Solver can change to make D12 4 or less, so it comes back with "unable to find a feasible solution".

I don't understand what you are trying to do with this constraint, but I would suggest that you need to think it through more carefully and edit the spreadsheet or the constraint accordingly.