You can control whether PO selection is mandatory during GRN creation through Store Settings. By enabling Mandate PO selection during Purchase option under Settings/ Store Settings/GRN Settings, the system will allow GRN creation only if a Purchase Order (PO) is selected, ensuring proper purchase tracking. If PO selection is not mandatory for your process, simply uncheck this option to create GRNs with / without linking a PO.
If the Mandate PO is selected you will not be able to create GRN without linking a PO
