PO re-allocation to an SO

I cannot allocate another PO from the SO. See below message. Please advise

It advises its pre-allocated.

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Doesn’t looks like a standard functionality? What action is triggering that info?

Thanks for getting back Kranthi. It triggers when I to allocate PO against an SO.

Scenarios explained below in detail…

Created SO-*123 & from this SO we created bac to back PO-*456.

After that we deleted the SO-*123 & now we want to link PO- *456 with another SO-*789.

This looks like a custom functionality. Check with your developer.