2d array isn't declared even though I declared it

I have this code right here which creates a 2d array which is initialized after the class and monobehavior (I don't remember this part name)

         [SerializeField] public int[,] priceManager;

I initialized the array in a method within Start() method this way:

         public void Method1()
         {
            priceManager[product.id, 0] = product.price1;
            priceManager[product.id, 1] = product.price2;
            priceManager[product.id, 2] = product.price3;
            priceManager[product.id, 3] = product.price4;
            priceManager[product.id, 4] = product.price5;
         }

The 'product' items are suppose to return integers. I have checked them and they are all correct. However I try to access this data from another method but the method doesn't recognize the array after filling in the values in the first method.

         public void Method2()
         {
            Debug.Log(priceMangaer[1,0]);     
         } 

Thus gives me this error:

         NullReferenceException: Object reference not set to an instance of an object

I can't see what's wrong and I am stuck on it. What went wrong?