I can't re-register Lightroom 6

[Szymon Zdunczyk]

Hi!
I purchased a license for Lightroom 6 on a Polish auction site in 2019. 
I received a link to the Adobe site, a license key, and an invoice. 
I installed the program on a desktop computer. 
Lightroom has been activated and registered with my Adobe account. 
I bought a new, faster computer and uninstalled the program from the old computer. 
I installed the program on a new computer, but I cannot register it. 
I get a message that the license is from an illegal source and I need to ask Adobe for a replacement 
serial number. Currently, Adobe does not support Lightroom 6 and I am unable 
to contact technical support. Only the forum is available. 
I can't use the program now and Adobe won't let me get a new license even though it originally 
registered Lightroom to my Adobe account. Has anyone been in a similar situation? 
Is there any solution to this matter?
Thank you

[dj_paige]

https://helpx.adobe.com/creative-suite/kb/error-serial-number-valid-product.html

[Ian Lyons · Accepted solution]

You could try contacting @CMass in the Lr 6 Activation or Deactivation thread at https://community.adobe.com/t5/lightroom-classic-discussions/p-activation-or-deactivation-versions-o...

[Rob_Cullen]

I purchased a license for Lightroom 6 on a Polish auction site in 2019.

Then you needed to also have the seller arrange a Transfer of Licence as Lr6 was not officiallly sold or supported after 2017. TRANSFER LICENSE 

I get a message that the license is from an illegal source

Quite possible you were scammed by the seller.  

See "What are Invalid Serial Numbers" at this link-  https://helpx.adobe.com/uk/genuine/faq.html

ask Adobe for a replacement seial number.

Not possible. Never has been.

Is there any solution to this matter?

For you- I do not think so!

Only an upgrade to v12.2 by subscribing to the Photography Plan (20GB) will restore your use of Lightroom (now called Lightroom-Classic)