The main question here is when you use PayPal, did you make payment? The system will only send emails after payment completed
So if you don't make payment when you are redirected to PayPal, no email will be sent
If you make payment, could you please access to Payment Form -> Payments, check to see whether there are any payment records related to that payment there? If Yes, what's the status of the record? Pending or Paid?
That mean PayPal could not notify the system about the payment yet and that's the reason causing the error
Is your site public accessible (not on a local computer, not in offline mode, please)?
You can login to your PayPal account (which received payment), access to this page
, check to see whether there is any IPN message related to your payment, click on it to edit and send me the screenshot of that message details. I will look at it and guide you to correct it further
mc_gross=35.00&protection_eligibility=Eligible&payer_id=WR3X6UAFJ3GP2&tax=0.00&payment_date=15:37:06 Jan 09, 2019 PST&payment_status=Completed&charset=windows-1252&first_name=Ron&mc_fee=1.32¬email@example.com&quantity=1&verify_sign=A5UBM41vuIk..JitVg8NUICXo59EAUYRUJRQR0qa9vSLCP-y3FHnfppifirstname.lastname@example.org&txn_id=5V989854667670933&payment_type=instant&last_name=Pettigrewemail@example.com&payment_fee=&shipping_discount=0.00&receiver_id=UH2HFDREFMQGS&insurance_amount=0.00&txn_type=web_accept&item_name=Payment for SARA Membership&discount=0.00&mc_currency=CAD&item_number=&residence_country=CA&shipping_method=Default&transaction_subject=&payment_gross=&ipn_track_id=17fdc1c23abb2