I don't know if it is worth creating a flag if there are no more problems at the moment, but you have much more experience than me in these matters.
I don't think this calls for a flag. He seems to be paying eventually, so there is no outstanding obligation / breach of contract (basis for type 2 or type 3 flag). There probably isn't a high risk of losing money (basis for type 1 flag). There is however (IMO) a high risk of not getting your money in a timely manner and there is misleading information on the website about how they handle their wallets. That's my thought process anyway ATM.
is late payment really a good reason for a negative tag? it doesn’t matter if it’s a signature campaign payment or a casino withdrawal.
as far as I could see, he did not give any excuses about casino withdrawal delay, nor any accusations against users or an attempt to avoid payment. I guess users of its casinos should be alerted to the probable possibility of late payment, but not that they will run out of their money. it seems to me that there is an important difference.
Red trust does not necessarily mean that money has been lost. That would the subject for a type 2/3 flag.
So the question really is whether it's a "high risk" to deal with someone who tends to pay late after much prodding, or someone who doesn't seem to have a contingency plan for their business (while implying that they do).
Can we negative mark them because of the low payment rate in their signature campaigns? I mean, it is below any minimum, and directly affects the production of spam on the forum.
Payment rate is part of the deal. Getting paid late is not. This is not about spam (not a concern for the trust system), it's about money being owed.