You can see who has an outstanding invite by looking at the Members & Teams page.
To re-invite users, you can either enter their email address on the Invite page or follow these steps below.
Only Workspace Managers can reinvite users, unless you've been provided permission.
Click on the "cog-wheel" icon in the top right corner of the page to open the Manage Workspace menu.
Select "Members & Teams" from the drop-down menu.
Under the page heading (Manage-Members) change the “Show” from Members to Invited Users.
Check the tick box/s of the people you wish to re-invite.
Click on the "Invite" button.
You can't re-invite people within 1 hour of inviting them!