You have to contact them to let them know. Use the phone number on their website and explain it to the person who answers. I was advised to email compliance AT paypal.com. Here's the partial text of the email:
Subject: Future unusual activity in my account
Hello, I called in to customer service and was advised to email you in order to avoid having my account suspended for unusual activity. I'm doing a big marketing promotion in the last week of February until the middle of March. As such, there will be large amount of funds going through my account over the three-week period. I estimate it will be between $10,000 to $20,000 over the three-week period. Thank you.
I received a generic response, but never had issues with funds being placed on hold.
