On the cic website they say:
"When we receive your application for citizenship, we review your application to make sure you:
- answered all the questions on the form
- sent all the required documents
- paid the fees
If you did, we send you an acknowledgement of receipt (AOR) letter. That means your application is ready to be processed. Your unique client identifier (UCI) is in the AOR letter.
If your application is missing information, documents or the fee receipt, we won’t accept your application and we’ll send it back to you. Once you get the missing information, you can resubmit your application."