Can't connect to WAC Gateway server - "Requested HTTP URL was not available"

v2211

I'm setting up WAC Gateway on a WS2019 server. Seems I can connect to all servers and desktops from it, except the gateway server itself. When I do, I get this message:

"Connecting to remote server <server.domain.local> failed with the following error message : The WinRM client sent a request to an HTTP server and got a response saying the requested HTTP URL was not available. This is usually returned by a HTTP server that does not support the WS-Management protocol. For more information, see the about_Remote_Troubleshooting Help topic."

FWIW, I can establish a remote PS session against the gateway server from another domain member.

Ran WinRM QuickConfig against the gateway server, no change.

Not sure what other information to provide, but output from winrm get winrm/config/service follows, if that's useful--

PS C:\Windows\system32> winrm get winrm/config/service
Service
RootSDDL = O:NSG:BAD:P(A;;GA;;;BA)(A;;GR;;;IU)S:P(AU;FA;GA;;;WD)(AU;SA;GXGW;;;WD)
MaxConcurrentOperations = 4294967295
MaxConcurrentOperationsPerUser = 1500
EnumerationTimeoutms = 240000
MaxConnections = 300
MaxPacketRetrievalTimeSeconds = 120
AllowUnencrypted = false
Auth
Basic = false
Kerberos = true
Negotiate = true
Certificate = false
CredSSP = false
CbtHardeningLevel = Relaxed
DefaultPorts
HTTP = 5985
HTTPS = 5986
IPv4Filter = 192.168.254.1-192.168.254.254 [Source="GPO"]
IPv6Filter [Source="GPO"]
EnableCompatibilityHttpListener = false
EnableCompatibilityHttpsListener = false
CertificateThumbprint
AllowRemoteAccess = true [Source="GPO"]