I've finally been able to deploy Forem on Heroku thanks to @akhil . However, I've a problem with it. I've setup Cloudinary and Amazon S3 Api variables on Heroku and I was able to use them. Then, I created a Welcome thread and add a cover image in it but it cannot be displayed. My Cloudinary account is not a paid account, it is the free one. I think that it might be the reason of this problem but I'm not sure. Do you have an idea about that?
You can check my forem instance and welcome thread by following the link below.
The cover image link that is defined as an src attribute: