cant update to ios18 from ios17.7

I updated my iPad pro m4 to ios 17.7 however im not able to update it to ios 18. There is no option for me to download the new os. It just says my ipad is up to date. I was able to download it last might but when i tried installing at the same time i was updating my iphone 14 pro max, my ipad update showed error “unable to update”.