Important Notes:
You have to be an owner of the SharePoint.
You have to be in the SharePoint site itself.
When you add the member, you must press type the email fully and press Enter and not select any autofill options.
1. Log into the SharePoint site you would like to add members to.
2. Click the Settings (Gear) icon on the top right.
3. Click Site Permissions.
4. Click Advanced Site Permissions.
5. Click the Site Members.
6. Click New.
7. Type the full email address and press Enter.
a. DO NOT SELECT THE AUTOFILL OPTION!
b. You can add multiple emails in this box. If you do, type each of the emails fully and press Enter each time for each email.
8. Click Share.
9. The user will receive an email saying that they are invited.