What happens when you tick it?

it just takes the tick out again and says sage cloud is required which is what we are on

The message refers to you needing to be on Sage 50cloud before turning on the feature.

Sage 50 Accounts and Sage 50cloud Accounts are two different things

If you've recently purchased Sag50 Cloud Accounts you'll need to put the key in by going to Tools > Activation > Upgrade Program. or if you're not on Sage 50Cloud Accounts you'll need to ring Sage's sale team to upgrade 0800 33 66 33.