how to use heroku rediss in a nestjs application

Question

I, recently, upgraded my data plan from mini to premium in redis, which came with a surprise i.e. "Heroku Data for Redis" add-on no longer exposes both redis and rediss protocols, but defaults to rediss only, which would be fine if Heroku did not use self-signed certificates for redis.

I have an existing NestJS application and the relevant part in it look as follows:

// in app.module.ts

import { RedisModule } from '@liaoliaots/nestjs-redis';

RedisModule.forRootAsync({
      imports: [],
      inject: [],
      useFactory: () => ({
        config: {
          url: process.env.REDIS_URL, // this starting with rediss::
        },
        commonOptions: {
          tls: {
            timeout: 10000,
            rejectUnauthorized: false,
            requestCert: true,
          },
        },
      }),
    }),

This unfortunately, give mes the following error: Error: self signed certificate in certificate chain

I have tried setting NODE_TLS_REJECT_UNAUTHORIZED to 0, which solves the issue locally, but on heroku, it then gives the following error:

Error accepting a client connection: error:1408F10B:SSL routines:ssl3_get_record:wrong version number

I have not been able to find information on the latter one, and still I'd prefer not to have to resort to NODE_TLS_REJECT_UNAUTHORIZED. Maybe someone can point me in the right direction?