Follow the below steps to create an additional user for a client,
1. Login to TargetBay admin panel
2. Click Accounts and choose desired account from the list
3. Click "Add User" button as in the screenshot - https://nimb.ws/2VSBJy
4. Fill all the details and click "Add user" to confirm the secondary user added to the mentioned account - https://nimb.ws/3HrziA