Solver not optimizing!

What do you expect the optimum solution to look like? I often find, when debugging something like this, that I need to know the solution to this specific problem in order to explore how the solver algorithm is failing to find that solution.

The only constraint I have is that 'Total Orders' should equal 'Total Order Planned' (B11=$B$2, red)

It shouldn't matter much to Solver, but I frequently set this sort of thing up so that B10 =B2-SUM(B5:B9), and then only change B5:B9. The constraint is now hard coded into the spreadsheet instead of needing Solver to manage the constraint.

Another thing I notice is that small changes to B5:B10 make very small changes to B15. I would not be surprised if Solver thinks that it cannot find a better solution because B15 does not change very fast. To some extent, this can be controlled in Solver's settings, but sometimes when the OF is changing too slow, it is just difficult to get Solver to find a solution.

If I've understood the model correctly, it looks like B15=B14/D11. B14 is a fixed value, so the maximum value for B15 is going to be where D11 is at its smallest. It might be easier for Solver to find the minimum of D11 rather than the maximum of B15 -- except that D11 can be 0 (resulting in a Div/0 error) at its smallest. What constrains the overall problem so that the optimum is not at D11=0?

You don't need Solver for this problem.

Maximizing KPI is like minimizing cell C11 (since we don't care about the constant value of 80$). C11 is a weighted average, therefore your best option is to set all the orders in cell B5.

If you really want to use Solver, you can minimize directly cell D11 (because the sum of orders is constrained to be equal to a given value), and set Simplex as engine.

I have removed cells B6:B8 from variables, since unit cost is zero.

HTH,

Francesco