I would look into integrating directly with Fulcro's network layer by creating a http-remote and configuring it with request and response middleware. That way you can let Fulcro deal with the low-level networking. https://book.fulcrologic.com/#_creating_a_remote

I put together a small js only fulcro app that talks to wikipedia's api, this uses pathom resolvers that return promises: https://github.com/dvingo/pathom-client-wikipedia/blob/master/src/main/dv/pathom_wp/client/application.cljs

I've been quite happy with promesa: https://funcool.github.io/promesa/latest/user-guide.html