PayPal payments are now only approved automatically when they were sent to the account in the PayPal Email setting. Other addresses can be accepted with the wp_job_manager_spl_paypal_accepted_emails filter.
PayPal payments must also match the configured currency and listing fee, and a PayPal transaction can only be applied to one listing.
Verify the server certificate for PayPal and Stripe requests.
Send the Stripe payment amount as a whole number of minor units.
Verify the preview form nonce and the listing being submitted when continuing to payment.