Re: about the payment details
1a is ambiguous. It is possible that the person is going to receive an email and the subject of that email is "payments details from PayPal". 1b is much clearer. The email about payment details will come from PayPal. Therefore, I prefer 1b.
Originally Posted by goodstudent
2 is fine.
Note that PayPal contains two capital letters. It's a brand name so you should stick to the way they write it.
Remember - correct capitalisation, punctuation and spacing make posts much easier to read.