Are you downloading through the Itch app? For some reason that doesn't work. But downloading using the normal website does.
Viewing post in Our Life: Beginnings & Always - Step 3 DLC comments
In that case you may have to contact Itch support. Unfortunately, we only upload the files to their site and can fix problems in the files. We can't access their site back end to make their download system work. Using another browser type or just waiting to see if it's a blip that'll go away tomorrow are things you can try if you don't want to reach out to them.