Is this correct grammar - We have already informed you that?

"We have already informed you that..." is grammatically correct, but it's incomplete. It's a dependent clause, meaning it needs an independent clause to make a complete sentence.

Here are some examples of how to complete the sentence:

* We have already informed you that the meeting will be held tomorrow.

* We have already informed you that your order is being processed.

* We have already informed you that you have won the contest.

Essentially, you need to add a phrase that explains *what* you have informed them about.