Who Me Too'd this topic

I'm deeply regretting my 628x purchase in 2019 (still under warranty I believe) since Netgear seems to have completely abandoned ReadyNAS product. Debian Jessie is old has also been archived.  They really should OpenSource ReadyNAS OS6 so the community can release future updates.  :::PLEASE PLEASE!:::

Anyway, I'm having a couple of problems which I can't seem to fix: 

$ apt-get update

W: GPG error: http://mirrors.edge.kernel.org/debian jessie Release: The following signatures were invalid: KEYEXPIRED 1668891673
W: The repository 'http://mirrors.kernel.org/debian jessie Release' is not signed.
N: Data from such a repository can't be authenticated and is therefore potentially dangerous to use.
N: See apt-secure(8) manpage for repository creation and user configuration details.

The next is: 

apt-get -qy install build-essential ca-certificates libreadline-gplv2-dev libncursesw5-dev libssl-dev libsqlite3-dev tk-dev libgdbm-dev libc6-dev libbz2-dev python-software-properties software-properties-common git-core python2.7
...after several successful Get packages... it terminates with:

E: Failed to fetch https://apt.readynas.com/packages/readynasos/dists/6.10.8/main/pool/l/linux/linux-libc-dev_4.4.218.1_amd64.deb Hash Sum mismatch

E: Unable to fetch some archives, maybe run apt-get update or try with --fix-missing?

 I'm not sure how to solve these... Hash Sum mismatch?  Is there a problem with the distro?  Any help is greatly appreciated!!  Thank you.