I have a CPLEX model that has the error "Not an array type" but I cannot figure out the issue. Please give insight

I have put together a CPLEX model that refers to data in an excel spreadsheet to optimize the number of officers we commission given resourcing limitations. I have managed to fix all errors except for one "Not an array type" error. I have marked the error in the below code using a comment to the right. It is in the Progression Dynamics section. I'm sure it is something simple I am overlooking but I have exhausted by newbie knowledge to figure it out.

// Sets
{string} MSL = ...;
{string} Type = ...;
{string} FY = ...;

// Parameters
float initPop[MSL][Type] = ...;              // Initial population per level and type
float gain[MSL][Type] = ...;        // External average gain into each level/year
float progressRate[MSL][Type] = ...;      // Progression rate to next level
float retainMSL[MSL][Type] = ...;  // Non-progression but retained
float CmsnRate[MSL][Type] = ...; // Cmsn rate
float costPerYear[Type] = ...;   // Cost per type

float budgetLimit = ...;
int capacityLimit = ...;
int mission = ...;

// Decision variables
dvar int+ cadet[MSL][Type][FY];       // Number of trainees per level/type/year
dvar int+ commissions[Type][FY];             // Graduates per type/year

// Objective
maximize sum(t in Type, y in FY) commissions[t][y];

// Constraints
subject to {

   // Progression dynamics
  forall(y in FY: y != "2026") {
    forall(l in MSL: l != "MSL1") {
      forall(t in Type) {
        // Progressed from previous level
        cadet[l][t][y] ==   //This is the location of the "Not an array type" error
            progressRate[prev(MSL,l)][t] * cadet[prev(MSL,l)][t][prev(FY, y)]
          + retainMSL[l][t] * cadet[l][t][prev(FY, y)]
          + gain[l][t][y];
      }
    }
    // Level 1 has only gain and retained
    forall(t in Type) {
      cadet["MSL1"][t][y] ==
          retainMSL["MSL1"][t] * cadet["MSL1"][t][prev(FY, y)]
        + gain["MSL1"][t];
    }
  }

  // Define graduates as those progressing from L4 to L5
  forall(t in Type, y in FY)
    commissions[t][y] == CmsnRate["MSL4"][t] * cadet["MSL4"][t][y] + CmsnRate["MSL5"][t] * cadet["MSL5"][t][y];

  // Budget constraint per year
  forall(y in FY)
    sum(l in MSL, t in Type)
      costPerYear[t] * cadet[l][t][y] <= budgetLimit;

  // Capacity constraint per year
  forall(y in FY)
    sum(l in MSL, t in Type)
      cadet[l][t][y] <= capacityLimit;

  // Minimum graduates per year
  forall(y in FY)
    sum(t in Type) commissions[t][y] >= mission;

}

I have addressed each individual error as it pops up in the Optimization studio. I even ran the error with a reference to the code through AI which made some good sounding suggestions but everything it suggested checked out.

What is not ok is that you wrote

+ gain[l][t][y]

But earlier you wrote

float gain[MSL][Type] = ...;  

So gain is a 2D array but you use this as a 3D array