Activities import for Opportunities

I see that there are a couple of topics out there for importing activities to various record types.

I’ve tried to follow the examples given, but I’m still running into an error. 

• Import AR Invoice Activity (type=Chat)

Along with the activity, I want to include the related document (which is an opportunity in this situation).

This is the error that I’m getting:

This is my import scenario (I’ll attach the xml at the bottom):

Any help is appreciated!