I’ve recently done the same thing. I setup both dendrite and synapse.
For both I tried the srv record and could not get it to pass the federation testers.
In the end as mines behind a nginx proxy I served the wellknows frommnginx rather than letting synapse/dendrite serve it. Federated correctly afterwards.
As such I would suggest serving the json well know using whatever reverse proxy you are using.
I’ve recently done the same thing. I setup both dendrite and synapse.
For both I tried the srv record and could not get it to pass the federation testers. In the end as mines behind a nginx proxy I served the wellknows frommnginx rather than letting synapse/dendrite serve it. Federated correctly afterwards.
As such I would suggest serving the json well know using whatever reverse proxy you are using.