I'm having this problem with an update to Baby's First Space Race I'm trying to host on DropBox. The link in particular is:
https://www.dropbox.com/s/vegt2950mc6ys4o/babys-first-space-race-1.7.10.5.zip?dl=1
When I try to change my modpack location URL to that, I get the dreaded "The Modpack Location you entered is not a valid location."