<html><pre>Dear community!
An OLD Sipwise GPG key that is used to sign repositories with NGCP and Debian packages expires on March 3rd, 2020.
So 'apt update' command would not work with the error:
=====================
Err:3 https://debian.sipwise.com/debian-security stretch-security InRelease
The following signatures were invalid: EXPKEYSIG 773236EFF411A836 Sipwise GmbH (Sipwise Repository Key) support@sipwise.com
=====================
You can find the update guide on Sipwise site https://www.sipwise.org/news/update-of-a-sipwise-public-gpg-key
</pre></html>