Quantity delivered differs from qty. invoiced (Function not possible)

What causes this issue?

You have attempted to delete an item whose GR and IR quantities differ.

How to fix this error?

You can only delete when processing has been completed. This means that
the delivered quantity of the goods must correspond to the invoiced
quantity.
You can eliminate the difference in one of the following ways:

The system issues an error message and will not allow you to continue with this transaction until the error is resolved.

Goods Receipt (GR) posting
Invoice Receipt (IR) posting
Maintenance of the GR/IR clearing account

Error message extract from SAP system. Copyright SAP SE.