Sellers can choose whatever payment method they like. BHW just funnels traffic to our own individual websites or sales pages.
If you think laterally, there is nothing stopping a seller from advertising their Telegram/Discord whatever group on their own website or sales page that is linked from their sales thread on BHW. Might even be an effective way to provide support for your product service that you're selling.
But as already said, you can't direct link.
Also to clarify, if you become a paid member and are therefore eligible to have a signature, you still can't link to any other forum/group chat etc. from your signature. You'll notice that pretty much all the signatures of members either link to internal BHW threads or external sales pages/websites.
Full rules can be found at https://www.blackhatworld.com/help/terms/
Hope this helps!
