Laravel save() returns true but does not change anything in the database

Question

I’m trying to do an UPDATE to change my user’s password, the function is returning me SUCCESS, but when I go in the database nothing has changed. I am doing a post via Postman, for the following route "http://localhost:8000/api/issuer/3", in my body I am sending the current password and the new password via x.www.form.urlencoded. When I do the validation if the current password is different from the one typed it returns me 'Passwords do not check' until then everything OK, but when it is to change the password via save() it does not change in the bank.

my route

Route::post("emitente/{emit}", "EmitsController@alteraSenha");

my model

  namespace App;

use Illuminate\Database\Eloquent\Model;

class Emit extends Model
{
    protected $table = 'emit';
    protected $fillable = ['senhaUsu'];    
    
}

my controller

 public function alteraSenha(request $request , Emit $emit){
    
    if(($emit->senhaUsu == $request->input('atual')) AND (!empty($request->input('nova')))){
        
        $emit->senhaUsu = $request->input('nova');
        
        if($emit->save()){ 

            return response()->json(['status'=>'sucesso']);
        }    
            
    }else{
        return response()->json(['status'=>'Senhas não conferem']);
    }  

}