Here's our recommended workflow for using D2L/Brightspace and Pivot Interactives.
From the Pivot Interactives website:
Create your class. However, do NOT invite students using a class key or link. More on why below.
Find some activities and add them to your library.
Next, go to D2L and create an assignment.
The first time you do this, you'll be asked to login to your Pivot Interactives account.
Select the class you'd like to link, click Connect.
Select the assignment you'd like to link, click Connect.
That's it! You won't have to enter your login credentials the next time you link an assignment.
When students click an assignment from within D2L for the first time, they'll be automatically placed into the correct Pivot Interactives class. No need for you to distribute a class key. This also ensures that each student's D2L and Pivot Interactives accounts are linked, ensuring that grades transfer successfully between the two.