Hey there,
I've made a modpack recently and everything was going well until this happened when updating it.
I have checked the link specified, and, it's right, I can't download it.
https://libraries.minecraft.net/com/typesafe/akka/akka-actor_2.11/2.3.3/akka-actor_2.11-2.3.3.jar
Is there a workaround or a fix for this?