When attempting to process a payment via a BBIS payment page, one may encounter the following error:
The underlying connection was closed: Could not establish trust relationship for the SSL/TLS secure channel
This is indicative of an issue with the SSL certificate. A few things to check:
1. Confirm the SSL certificate is not expired. 2. Confirm the SSL certificate is configured correctly. 3. Confirm the SSL certificate is in the correct Trusted folder. 4. Confirm the page is using https and not just http. 5. Check the firewall settings per KB 50865 (https://kb.blackbaud.com/articles/Article/50865). 6. Confirm the SSL certificate is properly imported to the web server. The certificate import may appear to import successfully, but upon inspecting the folder it was imported to, the certificate may not exist. This is indicative of a corrupt certificate. Download a new one and import it.