> What do you mean by synchronise the calls? like not calling the refresh api in parallel from one device with the refresh token?
Yes. It means that if two API requests that were made in parallel both return with a 401, only of them should call the refresh API whilst the other should wait for the refresh to finish. After refresh, both should retry the original request.
> and pass in the redirect the jwt token instead to the mobile apps?
You could. And then you would pass this JWT in each API request from the iOS app.