Join meeting using Lync Web App resolves to internal

Question

Vanilla Lync deployment: 1 FE (Standard Edition), 1 Edge, 1 Reverse Proxy (IIS 8, ARR 3.0), 1 Office Web Apps Server
When I send out a meeting invitation to an external user and they click on Join Meeting, the resulting link "Join Using Lync Web App Instead" points to my FE server.
I've got the External web services FQDN defined in Topology Builder:
'lyncweb.domain.com', but when I go to install Lync Web App, it says it can't find 'lyncfe.domain.local'
Looking at the URL for the 'Join Using Lync Web App instead' I see:
"https://lyncfe.domain.local/lwa/WebPages/LwaClient.aspx?legacy=..."
My reverse proxy has server farms set up that all point to my FE server, as prescribed.
Another issue I think is related: I have 2 simple URLs listed for meetings: meet.domain.com AND meet.domain.local; both show as active. Do I need the internal URL? If not, I can't remove it. I tried but after I highlight it and click on remove, it just puts
a red box around the field and greys out the OK button.
So I thought, maybe that's because I have 'domain.local' defined as a SIP domain. So I checked there and, yes, I do. And it's the
Default SIP domain. I have 'domain.com' listed as an additional SIP domain.
I thought about changing the default to 'domain.com' but found an article (http://lyncuc.blogspot.com/2014/04/change-default-sip-domain-in-lync.html) which says DON'T DO
IT.
So...?
"Never, ever doubt what nobody is sure about." -Willy Wonka

Answer 1

Confirm that the External Web Services FQDN for the Lync Front End pool is not defined anywhere else in the topology, must be unique. Seen people use the same FQDN as their Edge server.
Confirm External Web Service FQDN is on the SAN list for the Reverse Proxy Certificate and the Lync Front End Certificate.
Please mark posts as answers/helpful if it answers your question.
Blog
Lync Validator - Used to assist in the validation and documentation of Lync Server 2013.