invalid signatures EXPKEYSIG

sorry if I did something dumb but I'd really appreciate some help.

this comes up whenever I try to check for updates

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.opensuse.org/repositories/home:/strycore/xUbuntu_18.04  Release: The following signatures were invalid: EXPKEYSIG 2F7F0DA5FD5B64B9 home:strycore OBS Project <home:[email protected]>
W: Failed to fetch http://download.opensuse.org/repositories/home:/strycore/xUbuntu_18.04/Release.gpg  The following signatures were invalid: EXPKEYSIG 2F7F0DA5FD5B64B9 home:strycore OBS Project <home:[email protected]>

Moderator Note: The wget link here is no longer operational as that repository no longer publishes Ubuntu 18.04 repository lists or key data. However, the content of this post was left alone for historical reasons, and should not be flagged as 'broken link' in reviews.

You have to visit the repository page and re-add the repository signing key again:

wget -nv https://download.opensuse.org/repositories/home:strycore/xUbuntu_18.04/Release.key -O Release.key
sudo apt-key add - < Release.key
sudo apt-get update