I FOUND OUT what links reddit accepts in the Reddit module on make.com
ANSWER ON HOW TO FIX THE PROBLEM:
You need to first upload images to the AWS server belonging to Reddit using an HTTP request, having received a link to your image from AWS. And you need to send this link to the URL of the “Reddit” module - in this case, the post will be created and you will no longer receive the error “[[“BAD_IMAGE”,“Invalid image URL.”,“url”]]”
Example correct URL for Reddit module:
https://reddit-uploaded-media.s3-accelerate.amazonaws.com/[your_ID_of_image]
You should create your credentials on the Reddit API website (Reddit - Dive into anything), having received a Client ID and Client Secret (plus username and password your reddit account) to use them when sending images to the Reddit AWS server.
I don’t have a simple solution yet on what HTTP request to create (how to fill it) in make.com, but you can create such a link yourself using PRAW (after doing some research on how it does it) or using this simple JS program that also takes the solution from PRAW - https://www.npmjs.com/package/reddit-api-image-upload?activeTab=readme
This link has a full explanation of how reddit works in terms of image uploading.
When I have a full automated solution (based on HTTP requests) for make.com, I will add to my post here =)
Example app on reddit:
