Is Fill & Sign not available in Acrobat Pro? "You do not have access to this service."

I use the Adobe Teams Admin Console to purchase licenses for my compahy. 

Some users in my company only need Standard, and some need Pro. 

All Standard users are able to use the Fill & Sign -> "Get others to sign" feature to request signatures. 

Some Pro users - not all - receive an error when they click "Specify where to sign": "You do not have access to this service. Please contact your IT administrator to gain access." 

What do I need to do to give Pro users access to request signatures?