Try running a keyword search through the files of your website for “Google_Client”. I did this and found that a plugin called “Duplicator Pro” that I use to easily migrate websites was interfering giving the same error you’re receiving. After I deactivated / removed duplicator temporarily, I was able to activate Google Sheets plugin successful. Hope this helps.
Thank you for the advice. Since posting this, I have figure out a temporary solution to the issue. Through keyword search I discovered another plugin (Duplicator Pro) was also using Google_Client. After deactivating / deleting the Duplicator Pro plugin, I was able to activate cf7 google sheets.
