PDFs will not combine

I have paid for Adobe Acrobat and am supposed to be able to combine PDFs.  I am directed to the link https://cloud.acrobat.com/combinepdf and I am able to upload all the files I would like to combine, but there is no way to actually combine them.  The "Combine" button appears to be inactive. 

Please help. 

Unsure why I am paying for a service that does not seem to work when I need it to and I should get some money back for every day it goes without working.

Thanks,

Regina