@zOrlAc
I've analyzed this again and you're only partially right:
When you do rightclick on a file/folder in the seedr.cc interface, you can do two things:
1. Clicking on download will start the download via browser right away.
2. Clicking "Copy Download Link" will just copy a download link which you can e.g. download using JDownloader.
The 2nd option seems to be broken and returns an invalid URL - just test it via browser

Here is a screenshot:
Here is a workaround for you:
1. Make sure your seedr.cc account is active in JDs account manager.
2. Instead of adding these broken direct-URLs, go into the folder that you want to download and add this kind of URL to JD:
seedr.cc/files/123456789
This will let JD parse the files internally and use their not-broken "Download button"

Also, this is the way to usually use JD and if you ask me, this way is actually more comfortable than the way you have been doing it so far
If you want their "Copy Download Link" to work again, please contact their support and ask them to fix it.
-psp-