IPSEC transport does not work through GRE. And just an IPSEC tunnel, are the ports closed?

Question

Mikrotik

Hello. I create a banal tunnel through GRE. It's just that the GRE tunnel works, the traffic runs. As soon as I add IPSEC everything dies.
There is no SA, more precisely, only one, auth and enc are none.
There is a connection in remote peers, the status is message 1 sent.
One on both routers.
There is also a third point, it works fine with, say, the second point. And here the first with the second point does not want to work.
Ports blocked at the provider?

Answer 1

UDP port 500 was closed. I had to change the provider, because they refused to open it, like many other ports.