Having members or users linked to your account is an exclusive feature for the business plan. So if you are on a basic or a starter plan you must switch first to a business plan by:
1. As the account admin go to admin management page on the side menu
2. Select Plan & billing
3. Click on Change plan
4. Select Business plan
5. Select your number of licenses
6. Click on Pay now. If you are already on a business plan then to add more users you must add an equivalent number of licenses. you can do that by:
1. As the account admin, go to admin management page on the side menu
2. Select Plan & billing
3. In the user licenses section click on manage
4. Select Business plan
5. Select your number of licenses
6. Click on Pay now
7. Go to the Users page from the side menu and add your users