The error seems to indicate that the ZIP file that was download is not a valid ZIP. I think it is unlikely that the file on the server is invalid as otherwise it would not work for anyone. So I guess maybe it got corrupted during the download and the easiest solution might be to just try again.
Nevertheless this was forwarded to the premium support team who will have further help in case this doesn’t fix it.
Can you download the plugin from your account and unzip it locally? Does this work? If so copy the contents to the plugin directory of your Matomo /plugins/SearchEngineKeywordsPerformance
I can’t download the plugin because the treasurer of our Society bought it. I’ve wrote him a mail he should download the zip file and send it to me. Then I will try to copy the contents into the folder.