Can someone explain what in the heck is this? I paid already the license! 

Vs. 3.4.x 

 

That is version 3 of IP.Board, which was retired long ago and no longer works with our licensing system, unfortunately.

When you upgrade to version 4 , that error won't happen.

Just to add on to what Mark said, while you are more than welcome to use your software on version 3, it is extremely recommended to upgrade to the latest release of version 4 as version 3 is no longer in development and no longer receiving security releases or bug fixes.  Let alone the infrastructure (PHP, MySQL, Apache, etc...) which is required to run version 3 also is no longer supported by their respective authors so it is highly recommended to upgrade our software and your infrastructure so you are not at risk, and receive bug fixes, support, etc...

Yeah, well thanks. 

That whole platform was made for 3.4.x. Moving to 4.x.x will destroy everything (templates, plugins etc.) and I don't have neither the time nor the mood to change all of them.

Question: Why do I pay for the license if that version is not anymore supported??? Where is the catch? Am I missing something here? 

Your renewals give you the spam service, the ability to download the latest releases, access to client related area etc. Not just support. With regards why you pay for renewals when you are not upgrading your site from an unsupported version,  there is only really yourself who can answer that question. Our advice would be to upgrade. The version you are using there has not been supported for years, and isn't even supported for security related issues. The choice not to upgrade is entirely your own there