System.Net.Sockets.SocketException (0x80004005): A connection attempt failed because the connected component did not respond correctly after a period of time, or the connection failed because the connected host did not respond ***.***.***.***:55340
in System.Net.Sockets.TcpClient.Connect(String hostname, Int32 port)
in InSimDotNet.TcpSocket.Connect(String host, Int32 port)
in InSimDotNet.InSim.Initialize(InSimSettings settings)

My project was working perfectly yesterday, but when I try to start it I have this problem and InSim doesn't start.

Does anyone have an idea what it could be?

Have you done /insim 55340 in lfs?
Either way, your application failed to connect to LFS.
Hard to say what it is without seeing a code snippet.

I looked at your host and see there are no IP addresses allowed to connect to InSim. You need to add your IP address in the "Access Control" section.

Quote from Scawen :

I looked at your host and see there are no IP addresses allowed to connect to...

I am trying to connect to a host that has not purchased S3 (booted from my computer). Has there been any change that means I can no longer start it locally, without the need to purchase the host?

There has been a change but it does not require you to purchase a host.

You must enter your IP on this page after starting your host: https://www.lfs.net/hosting/admin

Quote from Scawen :

There has been a change but it does not require you to purchase a host...

Thank you sir!! 🙏