You need a new vendor certificate for your REST API gateway users as your old one will expire soon.
The recommendation from Broadcom Cloud Ops is to add all of the Root CA certificates from https://www.digicert.com/kb/digicert-root-certificates.htm. If preferred, you can add only the Intermediate certificate that is the issuer of Broadcom's current server certificate and the new server certificate that will be applying. Broadcom has verified that both the current server certificate and new certificate were issued by the following CA chain, whose certs can be found on the referenced page:
***Please note this is with the understanding that the Intermediate CA could change in the future.