One person cannot connect to server while others can

I've been attempting to set up a Forge server for my friends and I for about a week. I've just been trying out different mods and all of my friends except for one have been able to join. I do not port forward, and I use PlayitGG for a tunnel. He is getting the error "Connection refused: no further information".

I had him set (with me monitoring) a static IP, make sure he had Java accepted in his firewall, and I also whitelisted him on the server.

Does anyone have any solutions or things I could try?
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