Yes IS extending setting should help resolve the issue.
In your IS 9.0 env, what was the current setting you have for enabling TLS1.0?
I hope you have these in place on your DMZ IS or Internal IS outbound to enable various versions of TLS?
watt.net.jsse.server.enabledProtocols=TLSv1,TLSv1.1,TLSv1.2
watt.net.jsse.client.enabledProtocols=TLSv1,TLSv1.1,TLSv1.2
watt.net.ssl.client.handshake.maxVersion=tls
watt.net.ssl.client.handshake.minVersion=tls
watt.net.ssl.server.handshake.maxVersion=tls
watt.net.ssl.server.handshake.minVersion=tls
But I am not sure if the above will work for 9.0 or requires higher versions of IS 9.x.x
HTH,
RMG
#webMethods#Integration-Server-and-ESB#B2B-Integration