We have 188.8.131.52 (9.1.0) installed and are trying to update to 9.1.1 using apt-get on Ubuntu we are getting the following error:
W: An error occurred during the signature verification. The repository is not updated and the previous index files will be used. GPG error: https://download.owncloud.org/download/repositories/stable/Ubuntu_16.04/Release.gpg The following signatures couldn't be verified because the public key is not available: NO_PUBKEY 74AE7F72479BC94B
How can we fix this?