Build iso fails in 1.3.7 - Access error for (403)

this is my first post, apologies if I’m posting to the wrong channel. I’m trying to build vyos 1.3.7 (equueleus) using the docker build method as described in Build Vyos - VyOS 1.3.x documentation on Ubuntu 24.04. Searching the forums and the net didn’t bring me a clue. The sudo make iso build step fails with

E: Failed to fetch  403  Forbidden [IP: 443]
E: The repository ' equuleus InRelease' is not signed.

I didn’t have these problems building any other version of the equuleus branch before.
Appreciate any help or pointer

You will have to build the packages yourself unless its the 1.5-rolling you are building: