Donation Form

I am creating a Donation Form that links to an online credit card processor. I need the form to send the donor to a new page where either a confirmation message is displayed or an error message based on the returned fault code (invalid credit card number, decline, etc.) by the online processor. If the online processor sends a fault I would like to display/explain the error as well as have a link back to the donation page with the previous input fields auto populated based on the previously submitted data.

Currently I am using the "gform_post_submission" function to submit the data to the online processor but the entry is still being submitted and thus a notification email is being sent (to admin) as well as a confirmation message/page/redirect is happening based on form settings. How might I go about this as I'm a bit lost.

If I am correct then I would not have access to the entry data using the "gform_pre_submission"? I need this data to process the online donation transaction. The problem it that I need to convey to the donor whether or not their gift was accepted or denied and if denied then display the form again to have them fix the incorrect data.

Just thinking here but would it work to disable the notifications (gform_disable_user_notification) and post (gform_disable_post_creation) for this form until the online transaction(donation) is accepted and then submit/enable post and notification?

I see how this would allow me to validate data before it is sent but what would I need to do if I desired to send this data to a third party (processing merchant) and then based on their response (accept/deny) I would either show a confirmation page or re-display the form with text stating the error and auto-populated fields with previously submitted data. I would also like to get a response from third party (processing merchant) before a notification is sent (obviously would not send notification/confirmation if denied) as well as the submitted data posted to the WP Gravity Form database.