Hello everyone 
I’ve installed a Synapse server at synapse.first-domain.com, then I updated the DNS zone from my OVH control panel for first-domain.com by adding the following line:
_matrix._tcp.synapse.first-domain.com. 3600 IN SRV 10 0 8448 synapse.first-domain.com.
Then I installed a Riot application at chat.second-domain.com, (at the root: /), specifying that the server was synapse.first-domain.com.
And now, when I go on the Riot page, it just keeps loading, while saying I’m offline.
Also the URL when I go to chat.second-domain.com changes to https://chat.second-domain.com/#/room/!DoknAsPsVkbZafQyha:chat.first-domain.com
Which is odd because the “chat.first-domain.com” domain is not supposed to exists. Actually it does exist (there is a DNS zone for it) but will be used for a different purpose, completely unrelated with matrix, synapse or riot.
Also, when I click on the settings cog in Riot, I get this message:
CORS request rejected: https://chat.first-domain.com/_matrix/client/r0/profile/%40myusername%3Achat.first-domain.com
Which again is strange as I definitely specified when installing Riot that the server was synapse.first-domain.com, not chat.first-domain.com. This only chat dot something, is chat.second-domain.com.
Sorry if it is confusing, do not hesitate to ask me to reformulate if so.
Any idea then about what I’ve done wrong? Is the multi-domain a bad idea? Am I misunderstanding the whole logic of Riot and Synapse?
Still, thank you for supporting these amazing apps! (the latest Riot version looks yummy btw)