What might prevent a client from converting an estimate to a purchase order?

Choosing to enable purchase orders in the Account and Settings is crucial for a client who wishes to convert estimates into purchase orders. QuickBooks Online allows users to convert estimates into purchase orders when this feature is activated. If a client has not enabled this functionality, they will be unable to make that conversion, regardless of their subscription type, the version they are using, or the status of their other purchase orders.

In the context provided, other options do not directly relate to the ability to convert estimates into purchase orders. For example, while being on the QuickBooks Online Plus version is important for certain features, the ability to convert estimates specifically hinges on the purchase orders feature being enabled. Additionally, lacking an active subscription or having existing purchase orders would not prevent the conversion, as those scenarios do not affect the functionality of the conversion process itself. Thus, enabling purchase orders in the settings is the key factor for successful conversion.