Follow below Steps to allow Mobile App access permission to User,
Login into your CStore Essentials Account,
Click on the human-shadow icon on the Top-Right corner
Select Manage my Store
Go to Users
Find the particular User and on the right click on = Details button
Under Security Group Tab, Click + Add New Item
Add required Mobile Group:
Mobile Monitor
Mobile PriceBook
Mobile Lottery Scanning
Mobile Receive Delivery