Since we are new to the SSL thing, I had to check Google. There are a bunch of suggestions for you to try or check.
A couple examples suggest you're referencing the wrong intermediate certificate.
Google: Cert VALIDATION ERROR(S): unable to get local issuer certificate, certificate not trusted, unable to verify the first certificate
A couple examples suggest you're referencing the wrong intermediate certificate.
Google: Cert VALIDATION ERROR(S): unable to get local issuer certificate, certificate not trusted, unable to verify the first certificate