Changing exists rule based on choosen option

So i have this simple code to input value based on database value in registration form and it's work great,

The code below located at register.blade.php

1. This for selecting branch

   <div class="form-group form-material floating">
     <select class="form-control" name="branch" id="branch">
         <option value="1">Option A</option>
         <option value="2">Option B</option>
     </select>
     <label class="floating-label" for="inputStatus">Branch</label>
   </div>
   

2. This one for inputing reference

   <div class="form-group form-material floating {{ $errors->has('reference') ? ' has-error' : '' }}">
           <input type="text" class="form-control empty" id="reference" name="reference">
             <label class="floating-label" for="inputStatus">Reference</label>
             @if ($errors->has('reference'))
                 <span class="help-block">
                     <strong>{{ $errors->first('reference') }}</strong>
                 </span>
             @endif
         </div>
   

the code below located atRegisterController.php

3. And this one for validation

   protected function validator(array $data)
    {
   
    return Validator::make($data, [
   'name' => 'required|string|max:255',
   'email' => 'required|string|email|max:255|unique:users',
   'password' => 'required|string|min:6|confirmed',
   'phone' => 'required|string|min:5|max:20',
   'rate' => 'required',
   'product' => 'required',
   'branch' => 'required',
   'reference' => [
       'required',
           Rule::exists('references')->where(function ($query) {
               if( 'branch' == 1 ){
                   $query->where('references.type', '=', "TOP"); 
               }
               else{
                   $query->where('references.type', '=', "BOTTOM");     
               }
           }),
       ],
      ]
     );
    }
   

In registration form when user choose the first option on branch, the user can only write (Example : 'ABC', 'DEF', 'GHI') if the user write another value it will return Error Message : 'Wrong reference code', but when the user choose second option on branch, the user can only write (Example : '123', '456', '789'), , does anyone have and idea how to do it? Thanks