Is this stated anywhere on their website?
BetVoyager Tournaments
BetVoyager opens a series of tournaments with unprecedented conditions and a growing prize fund. Throughout the year players can enjoy mind-blowing prizes and adrenaline-boosting competitions. Anyone can be a winner, so hurry up and register in the upcoming Goldfish Bonanza Tournament with a €30,000 prize fund! Do not miss this unique opportunity!
To dismiss any doubts which players may have, the winnings can only be received upon one condition: the winners must make a publication regarding their win in the BetVoyager tournament.
The links to all the publications will be available on BetVoyager site.
If you look here hxxtps://www.betvoyager.com/tournaments/posts/ you can see all the winning posts and which forum they appear on, including one of the CM spammers, gyulas, who posted here, and then had the post altered and was banned for spamming.
The tournament rules are a little more specific....
How to receive tournament winnings
The amount of winnings is credited to the player's account strictly after he has made a publication regarding his win in the tournament on any gambling-related website (forum, blog etc). A player may use one of the posts templates, which can be found on the posts page or use his own text.
In essence, "make a publication" means "spam a forum with news of your win". Of course "may only be received" is the same as "will be confiscated if you don't" as far as players are concerned.
What players have to do to receive their prize is very simple indeed, sign up to somewhere where they can write a post about their win and then copy & paste a link to their post and give it to betvoyager. Presumably, they then check the link and award the prize.
It does not specify any preference as to which forum should be used, other than it being "gambling related", so only a few are choosing Casinomeister. The links can be checked without needing a betvoyager account, and a variety of forums are getting these posts.
Perhaps by taking robust action by banning those who do this here the word will get around the Betvoyager community to try a more receptive forum instead, one where you would be able to post several prize claims without having to sign up afresh each time as would be the case here.
Since Betvoyager staff are presumably verifying these posts before dishing out the prizes, you could use this to send them a direct message by editing the actual spam post so that it is made clear to the betvoyager staff doing the vetting that this is not tolerated, and they will be in your pit very shortly. They may not bother reading the rest of the thread and your eventual warning, and probably expect that some forum admins might edit such claim posts to remove links and advertising. However, so long as it's up long enough to verify a prize claim, neither player nor Betvoyager cares what happens to the post afterwards.