PayPal reserves the right to hold funds for up to 21 days, especially if you're a new account.

Here is a link for that article: https://www.paypal.com/us/selfhelp/article/how-can-i-get-my-held-payment-released-faster-faq1987
"Why is my payment on hold or unavailable?"

This is a direct quote from that link that I believe will answer your question: "1. You’re a new seller with PayPal or you’re an established seller but have opened a new account.
When you’re a new PayPal seller, it takes time to build up enough history to demonstrate a pattern of positive buyer-seller transactions. The good news is you can usually move out of this status by confirming your identity and building up a history of positive selling activity.
If you’re an established PayPal seller, but opened a new account, that account will be eligible for holds until a good history is established."