Here is the proper URL.
https://api.twitch.tv/helix/users/follows?to_id=403455113&first=100
It is not a problem of the library I am using. When trying it with wget I also experience problems.
However I think I might have identified a factor in this issue. I am located in Germany and my requests to “api.twitch.tv” end up somewhere in (probably) Frankfurt on the machine with IP 151.101.14.214. It might be a problem specific to the server there.
When I run my script from a VM in the Netherlands where api.twitch.tv resolves to 151.101.38.214 and probably ends up somewhere in Amsterdam it works just fine.