First select the items you require

What causes this issue?

You have either not marked any items or the function you require cannot
be executed for the marked items.
As a result, payments that have not been saved cannot be marked for
changes and payments already posted can be neither changed nor deleted.

System Response

Notice that processing cannot be carried out.

How to fix this error?

Mark items that are permitted for the function you require.

Error message extract from SAP system. Copyright SAP SE.