Error in apt-get update, 404's on "/xenial/main/binary-arm64/Packages"

Question

I have an nvidia jetson tx2, running sudo apt-get update, I get:

    Fetched 17.1 MB in 29s (577 kB/s)                                    
    Reading package lists... Done
    E: Failed to fetch http://ubuntu.mirror.cambrium.nl/ubuntu/dists/xenial/main/binary-arm64/Packages  404  Not Found [IP: 217.19.16.188 80]
    E: Some index files failed to download. They have been ignored, or old ones used instead.

I put the link in a browser, indeed it is 404. How do I fix this, what is the correct directory?