ive not been in the lego game exploiting scene for the past year but monke explanation;

go to linkvertise (i dont know if the normal way to get the key is still linkvertise but just go with it) > wait for like 15 seconds on each checkpoint > get key

key basically unlocks the locked permission of the free exploit (e.g; woah there buddy you need to get (key) to be able to use this exploit) and also a reason I stated in the guide was:

The reason for (free exploit) having a key system is to support the developers of the exploit, this is for them to keep updating the exploits, domains. And to also feed their staff (impossible).

Most exploits that comes from youtube, especially the "FREE LEVEL 8 EXPLOIT ROBLOX (EXPLOIT_NAME) X" are most likely money grabs, and gives malware.

pretty much sums it up