I'm all for letting them explain, but I think a red tag in the meantime while we wait is appropriate given what participants have complaints about. The tag can be removed if all turns out to be a misunderstanding.
Right, there's nothing wrong in tagging once you see a complaint and confirm it to be legitimate based on your assessments, I jus personally like to give a window to allow the user to respond first. @cryptomus_com has logged in now, but is yet to make a reply, so I'll safely assume they've read the complaints.
How they manage the situation withing the next few days will be very important to the future of the campaign and the project on the forum.