Change order request for material mix up
I install decking and railing on large apartment complexes. My contract consists of all material and labor. The Material is picked out by the general contractor and I just add it to my contract. Recently we were going over the details as the railing just showed up on site and his plans are different then what I received from the railing supplier. The general contractor had 10total posts on each deck but the railing supplier had only 4 using the columns and walls to tie into instead of end posts. I requested a change order to cover the extra costs of adding 6 more posts to each deck with a total of 54 decks. He declined my request and said I need to come up with the extra $19,000 in post cost to complete it as his plan shows, is this right?