Common App: only 1+2 = 3 slots to upload school transcripts?

It seems that common app has only 3 slots to upload school transcripts. What should one do if a kid has attended one regular high school and has taken classes at diff online high schools like Apex, BYU, US Scout and others.
How should one upload these (anything beyond 3) transcripts?
Thank you so much!

I would include the ones with the greatest number of courses on them and then note it in the Additional Information section, and then send the additional transcripts once you get your portal information.