Heroku addons:create --fork doesn't migrate redis data

I have an app hosted on Heroku and I am trying to migrate from Heroku Redis to Redis Cloud.

According to this documentation, I can easily migrate the data from my current Heroku Redis to a new Redis Cloud by using --fork flag.

https://devcenter.heroku.com/articles/rediscloud#migrating-from-an-existing-redis-server-to-redis-cloud

However, when I ran the command, it did create a new Redis Cloud instance but the instance doesn't have the data from my Heroku Redis instance.

This is the command that I used to create the instance

heroku addons:create rediscloud:100 --fork=`heroku config:get REDIS_URL -a app-name` -a app-name

Is the --fork flag only works for databases ?