Putting a customer on stop prevents their orders from being moved to any status other than 'Cancelled'. It will also prevent purchase orders from being created from their orders.

Quotes are also blocked by default but can be allowed using this setting in the Cog -> Module Settings -> Quotations:

Open the customer record and tick the 'On Stop'.

If this is not visible, make it visible using the field controller:

Learn more: jobs in Zigaflow