Optimization problem—constraints not valid? [closed]

Question

I have a model optimization problem: maximize rent, ri, through signals, si and sj, given someone's initial social position, SPi and SPj. Signals have a cost of 1, so the constraint is that D[ri, si] == 1 and D[ri, sj] == 1.

I get the error message

NArgMax::bcons: The following constraints are not valid:

....the whole equation for the constraint here...

Constraints should be equalities, inequalities, or domain specifications involving the variables. >>

I guess my questions are:

• Is the problem simply due to my parameters no allowing a solution within the constraint?

• Can I use the defined variables in the NArgMax inside signalFunc? (should they be defined as functions?)

Is NArgMax the right solution here?

α = 1000;
β = 0.03;
γ = 0.02;
m = 4000;
ω = 1;

ti = (α SPj (β sj - γ ((sj - si)/(sj + sj))^2 + 1)) + 
     (α SPi (β si - γ ((si - sj)/(si + sj))^2 + 1));
ri = ω (-(tr^2) + 2 m tr) /. tr -> ti

dsi = FullSimplify[D[ri, si], 
   Assumptions -> {Element[{si, sj}, Reals]}];
dsj = FullSimplify[D[ri, sj], 
   Assumptions -> {Element[{si, sj}, Reals]}];

signalFunc[{SPi_, SPj_}] :=
  NArgMax[{ri, dsi == 1, dsj == 1}, {si, sj}];

signalFunc[{0.8, 1.5}];