This issue will have to be resolved by the business partner as they are responsible for their certificates to their Core Server. Contact the corresponding business partner to have them investigate the certificate error. Once resolved test the SAL Gateway and ensure that the alarms are now reaching the Avaya Core Server.
Here an example of how the certificate looks like from an Avaya lab. In one case the customer had other certificate disturbing the Avaya certificate and changing the issuer field:
Server certificate:
* subject: CN=secure.alarming.avaya.com,O="Avaya, Inc.",L=Basking Ridge,ST=New Jersey,C=US
* start date: Jul 29 00:00:00 2021 GMT
* expire date: Aug 23 23:59:59 2022 GMT
* common name: secure.alarming.avaya.com
* issuer: CN=DigiCert SHA2 Secure Server CA,O=DigiCert Inc,C=US