Here's why:
* Missing Subject: The sentence lacks a subject. It doesn't specify who or what should "send." For example, it should be "Please send..." or "I will send..."
* Incomplete Thought: The sentence doesn't complete the thought. It needs to specify what should be sent. For example, "Please send me the information if you are interested."
Here are some ways to make the sentence correct:
* "Please send me the information if you are interested." (This specifies the subject and object.)
* "If you are interested, please let me know." (This avoids the need for sending anything)
* "I will send you the details if you are interested." (This clarifies who will be sending and what will be sent)