Indicator parameters to iCustom have no effect!

I wrote a custom indicator that looks like this:

#property copyright "Copyright 2022, Norbert Nemes"
#property link      "https://www.mql5.com"
#property version   "1.00"
#property indicator_chart_window
#property indicator_buffers 2;
#property indicator_plots 1;

#property indicator_type1 DRAW_FILLING
#property indicator_label1 "HMA Fast; HMA Slow"
#property indicator_color1 clrGreen, clrRed

input int period = 200; // Period of the moving average

double fastMA[];
double slowMA[];


//+------------------------------------------------------------------+
//| Custom indicator initialization function                         |
//+------------------------------------------------------------------+
int OnInit()
  {
   SetIndexBuffer(0, fastMA, INDICATOR_DATA);
   PlotIndexSetInteger(0, PLOT_DRAW_BEGIN, period);
   SetIndexBuffer(1, slowMA, INDICATOR_DATA);
   PlotIndexSetInteger(1, PLOT_DRAW_BEGIN, period);
   return(INIT_SUCCEEDED);
  }

...

It has a single input called period which determines the period of the moving average. Default is 200. I also have an expert advisor that is calling this indicator like this:

int OnInit() {
   profit = 0;
   stopLoss = 0;
   takeProfit = 0;
   previousData = "";
   hasBought = false;
   hasSold = false;
   tradeLine.Create(0,"Trade",0,0);
   tradeLine.Color(clrPurple);
   stopLossLine.Create(0,"StopLoss",0,0);
   stopLossLine.Color(clrRed);
   takeProfitLine.Create(0,"TakeProfit",0,0);
   takeProfitLine.Color(clrBlue);
   trade.SetExpertMagicNumber(123456);
   trade.SetDeviationInPoints(10);
   trade.SetTypeFilling(ORDER_FILLING_RETURN);
   boomerangHandle = iCustom(Symbol(),Period(),"Boomerang");
   volatilityHandle = iCustom(Symbol(),Period(),"VolatilityOscillator");
   hullHandle = iCustom(Symbol(),Period(),"HMA", hullPeriod);
   return(INIT_SUCCEEDED);
  }
//+------------------------------------------------------------------+
//| Expert deinitialization function                                 |
//+------------------------------------------------------------------+
void OnDeinit(const int reason) {
   if (boomerangHandle != INVALID_HANDLE) IndicatorRelease(boomerangHandle);
   if (hullHandle != INVALID_HANDLE) IndicatorRelease(hullHandle);
   if (volatilityHandle != INVALID_HANDLE) IndicatorRelease(volatilityHandle);
}

...

void createHMA(int count) {
   ArraySetAsSeries(hull, true);
   CopyBuffer(hullHandle,0,0,count,hull);
}

...

The problem is that no matter what value I pass in for the period, I keep getting data for the 200 (default) average. I looked online at the iCustom documentation and I think I'm calling it correctly. What am I doing wrong? I'm using mql5.