Pernah dapat error ni?
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/Debian_9.0 Release: The following signatures were invalid: EXPKEYSIG 47AE7F72479BC94B ownCloud build service
W: Failed to fetch http://download.owncloud.org/download/repositories/production/Debian_9.0/Release.gpg The following signatures were invalid: EXPKEYSIG 47AE7F72479BC94B ownCloud build service
W: Some index files failed to download. They have been ignored, or old ones used instead.
wget -nv https://download.owncloud.org/download/repositories/production/Debian_9.0/Release.key -O Release.key
2019-03-20 00:40:43 URL:https://download.owncloud.org/download/repositories/production/Debian_9.0/Release.key [4485/4485] -> "Release.key" 
apt-key add - < Release.key OK