Now i realized how important the receipt is it a correct grammar-?

The grammar is technically correct, but it sounds a bit awkward. Here are some ways to improve it:

More natural phrasing:

* "I realized how important the receipt is."

* "I now understand how crucial the receipt is."

* "I just realized how vital the receipt is."

More formal phrasing:

* "I have come to realize the importance of the receipt."

* "The receipt's importance has become clear to me."

The best option depends on the context and the tone you want to convey.