

Some users suggested some solutions over there on EA forums, one of which worked for me. In all scenarios, the message keeps appearing and the resources packs are not available in the DLC page. And trying to shut down both Steam and Origin, then booting the desktop icon, would launch both Origin and Steam. Trying to boot the game on Steam alone would boot it through Origin. Trying to boot the game on Origin alone would boot it through Steam. Whenever I tried to boot the game, a banner was displaying on Origin, saying: "The Origin store is currently disabled because it was launched from another application".

After you're done, you can keep playing on whatever operating system you usually use. TL DR: You need a computer with Windows 8.1 or higher in order to perform the solution below.

Might be that they decided to remove it completely, or their related servers are down/broken. I just now tested this, and it looks like my solution no longer works. UPDATE 6th September 2022: According to this post, the following solution doesn't work anymore, so ration seals can no longer be spent.
