Can one set up sign-ins for one account with different people having different emails and passwords, so that I don't have to share my master password with all the others?
HI, hopefully these Square Support pages will help. Team Management and Permissions.
https://squareup.com/help/us/en/article/5591-get-started-with-employee-management
https://squareup.com/help/us/en/article/5822-employee-permissions
You can create user Pins and also Device Codes so multiple device can access and take payments. You do not want to share you Account Email and Password as then those people have full Access to your account. By setting up User Pins you can create different levels of Access. Currently I have 3 devices that can take payments through the Device codes each is assigned and 4 user accounts, my wife, son, a generic Cashier account and mine.
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