When I sign up for these PTR sites, it asks for my account number, but I don't see an account number listed in my paypal account. Should I just leave the acct # field blank. If not, how do I find out the acct #?

I can't use paypal so I'm not sure but I think you use your email address that you signed up with paypal as your acct. #

Your Paypal account number is either the email address you used to sign up with Paypal, or one of the alternate email addresses that you have registered with them for receiving money.

OK, thanks. I signed up with Paypal using an email that is no longer valid. So I would use my current paypal email address, right?

If the address you signed up to Paypal with is no longer valid, I believe you still have to use it to sign-in to the Paypal site. That original address is like your permanent account number even if you no longer use it for email.

On the Paypal site you can add other email addresses (as many as 9, I think) so you'll be able to give them to vendors (like a PTR site) and get paid. When a payment is received, Paypal will send notice to whatever email address the vendor has used to send the payment to.

So give the PTR whatever email address you want them to use to pay you with, but first make sure you've gone to your Paypal account and added it to your list.