So I've had this issue for a couple of days. I went back and found the original email that I received when I created my PayPal business account, the one email in which I needed to click to confirm my account/email address. Once I clicked that button in the email, everything immediately popped up on my PayPal. Now have other issues that PayPal won't release money until it's shipped, but fixed the one issue.
I know this is an old post but hopefully it will help someone. I had the same issue. You may need to confirm your PayPal email. Log into PayPal and go to profile settings the personal information. Click on your email and there will be a little link under your email to confirm your email. After that you should get your money. If not you should get an email explaining why your Money is on hold. They will hold your money if they think you didn't ship your product out because maybe you just gave it to your customer instead of Shipping it. Then you will need print out a label on shopify or update the status of your product as delivered or completed in your Shopify account and it will be in your account after 7 business days after verification. I am not sure how they verify that though. Still figuring things out myself but I hope that helps!
If you ever get this be sure to log In to your PayPal account. It is likely they have limited the account from receiving payments. To rectify you need to fill in some additional info on the platform.
Sadly this issue has cost me money (refunds) and I am furious I had to discover the solution the hard way.
Best of luck