Does not work for me, I had production already in source list.
Maybe the signing got broken?
Cheers
Ulrich
root@ncc:~# grep owncloud /etc/apt/sources.list.d/owncloud.list
deb http://download.owncloud.org/download/repositories/production/Ubuntu_18.04/ /
root@ncc:~# apt update
Get:7 http://download.owncloud.org/download/repositories/production/Ubuntu_18.04 Release.gpg [481 B]
Err:7 http://download.owncloud.org/download/repositories/production/Ubuntu_18.04 Release.gpg
The following signatures were invalid: DDA2C105C4B73A6649AD2BBD47AE7F72479BC94B
All packages are up to date.
W: An error occurred during the signature verification. The repository is not updated and the previous index files will be used. GPG error: http://download.owncloud.org/download/repositories/production/Ubuntu_18.04 Release: The following signatures were invalid: DDA2C105C4B73A6649AD2BBD47AE7F72479BC94B
W: Failed to fetch http://download.owncloud.org/download/repositories/production/Ubuntu_18.04/Release.gpg The following signatures were invalid: DDA2C105C4B73A6649AD2BBD47AE7F72479BC94B
W: Some index files failed to download. They have been ignored, or old ones used instead.