Language: Node.js + Express

After implementing a custom login domain using the instructions here (https://developer.okta.com/docs/guides/custom-url-domain/update-other-okta-settings/) and updating each app settings to use the new domain, the last step was to update the "issuer" field when defining the OpenID Connect client in my node.js application. When doing that, I get the following error:

UnhandledPromiseRejectionWarning: RequestError: unable to verify the first certificate

  at ClientRequest.<anonymous> (C:\Users\*****\node_modules\got\source\request-as-event-emitter.js:178:14)

  at Object.onceWrapper (events.js:422:26)

  at ClientRequest.emit (events.js:327:22)

  at ClientRequest.origin.emit (C:\Users\****\node_modules\@szmarczak\http-timer\source\index.js:37:11)

  at TLSSocket.socketErrorListener (_http_client.js:469:9)

  at TLSSocket.emit (events.js:315:20)

  at emitErrorNT (internal/streams/destroy.js:106:8)

  at emitErrorCloseNT (internal/streams/destroy.js:74:3)

  at processTicksAndRejections (internal/process/task_queues.js:80:21)

The certificate is valid and if I access the custom domain URL via the browser there is no certificate error. If I return the issuer field back to the default, the error goes away. The only way I can get the application to use the custom URL is to add the environmental variable "NODE_TLS_REJECT_UNAUTHORIZED" = 0, which isn't safe long term for many reasons.

Any advice would be appreciated!