Welcome to the forum @chiragM !
I know the prompt tells you that you are submitting a “Pokestop” but you are actually submitting a Wayspot to the Lightship database, which can only become a Pokestop or gym if it is alone in a level 17 S2 cell. This is a good article about S2 cells and PoGo:
https://pokemongohub.net/post/article/comprehensive-guide-s2-cells-pokemon-go/
If you would like for us to check if it meets the L17 rule for you, you are welcome to post the name of the wayspot and gps coordinates. But if you don’t want to reveal your location, that is fine, too.