You try add new subcntracting components in the purchase order, however the Add Detail Entry is not available in the " Change Purchase Order Advanced" App or the " Create" Icon in " Manage Purchase Order " app.
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The Purchase Order already has a good receipt in the Purchase Order History Tab.
This is the correct behavior (works as designed). Changing or adding components after a GR posting would lead to inconsistencies. This would affect all further GRs. That's why it is not possible to change/delete or add components after the first GR.
This is the standard system behavior
KBA , MM-PUR-GF-SC , Subcontracting , Problem
SAP S/4HANA Cloud 2002