Update urls:
https://cdn.cloud-universe.anycubic.com/ota/prod/20023/AC104_k2MAX_V3.1.0.bin
https://cdn.cloud-universe.anycubic.com/ota/prod/20021/AC104_k2PRO_V3.1.0.bin
https://cdn.cloud-universe.anycubic.com/ota/prod/20022/AC104_k2PLUS_V3.1.0.bin
If you are on 3.0.9 you will need to install 3.0.3 first and then you can receive the 3.1.0 update.
Don’t know why they did this.