Google Sheets Script - Authorization Required/This app isn't verified - Explained
This short video adresses a question I've been asked a few times, relating to giving authorization to a script in google sheets the very first time you run it.
Keep in mind, this is a brand new sheet, and it was created in my own google drive. If you perform these same actions on a sheet which exists in someone elses drive, but is shared to you, the process will likely be different.