TOPIC: PayPal Instant Payment Notification Warning

PayPal Sent the Following, alerting us to the issue:
Please check your server that handles PayPal Instant Payment Notifications (IPN). IPNs sent to the following URL(s) are failing:

www.ncemsf.org/components/com_dtregister...77&task=notification
www.ncemsf.org/components/com_dtregister...77&task=notification
www.ncemsf.org/components/com_dtregister...77&task=notification
www.ncemsf.org/components/com_dtregister...77&task=notification
www.ncemsf.org/components/com_dtregister...77&task=notification
www.ncemsf.org/components/com_dtregister...77&task=notification
www.ncemsf.org/components/com_dtregister...77&task=notification
www.ncemsf.org/components/com_dtregister...77&task=notification
www.ncemsf.org/components/com_dtregister...77&task=notification
www.ncemsf.org/components/com_dtregister...77&task=notification
www.ncemsf.org/components/com_dtregister...77&task=notification
www.ncemsf.org/components/com_dtregister...77&task=notification
www.ncemsf.org/components/com_dtregister...77&task=notification
www.ncemsf.org/components/com_dtregister...77&task=notification

If you do not recognize this URL, you may be using a service provider that is using IPN on your behalf. Please contact your service provider with the above information. If this problem continues, IPNs may be disabled for your account.

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Additional digging on our end uncovered the fact that transaction IDs aren't being saved in DT Register.
Similar to this topic: www.dthdevelopment.com/index.php?option=...id=141&limitstart=15

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We've troubleshooted beyond the above, but are coming up blank. We need some help and hoping the community can pitch in.