Environment: Exchange 2010 on both sides, TMG2010 on my side (not sure about other side)

Exchange Federation is not working - not sure how to troubleshoot.  It doesn't work in either direction.

Test-FederationTrust shows all success
Get-FederatedDomainProof shows the proof, which has been created as a TXT file in external DNS
In EMC under Federation Trust, the gateway is configured (showing FYDIBOHF25SPDLT.domain.com) though the status is Unknown
In EMC under Organization Relationship tab, I can't connect via the automatic option (federation information could not be received from the external organization), but setting it manually gives no errors.

autodiscover is working fine according to https://www.testexchangeconnectivity.com/ - I can see the successes in TMG log when I run this tool.  However when I get a user in the domain I wish to federate with to get my free/busy via an Outlook Meeting Request, I don't see anything hitting TMG and they don't see my free/busy.

TMG rule is set to Basic Authentication

Where is the next area to troubleshoot?