i want to get form data from checkout page in 2nd step, so i have use event observer.

I have use this controller_action_predispatch_checkout event.

I want to get post data so i have try this https://magento.stackexchange.com/questions/166917/get-post-data-in-checkout-success-observer/166918 link but not able to get post data.

Can any one help me how can i get post data?