1.  Check the sales order type : SPRO -- > Salse and distribution -- > Sales -- > Sales Documents -- > Sales document Header -- > Define sales document types

2. configuration of Delivery block in SPRO: SPRO --> LE -- > Shipping -- > Deliveries -- > Define reasons for Blocking in Shipping (Deliveries:Blocking Reasons/Criteria)

Sales order type (Delivery block reason/criteria configuration in SPRO)