.cert vs .pem
Fellow Rocketeer Dillon Hafer had the explanation for my SSL issue mentioned at https://til.hashrocket.com/posts/c38666d448-react-native-heroku-and-ssl-heroku- reactnative -
"DNSimple gives you a cert and a pem file. The cert file is just the certificate, while the pem file is actually 4 certificates mushed into one file. The 3 extra certificates are the intermediate certificates required by some operating systems that only include Root Certificates. Hope that helps explain why the pem from DNSimple works while the cert doesn’t." - Dillon Hafer