If you get the error message [ESEF 3.3.1 extensionConceptsNotAnchored] it means that a taxonomy extension was used but not anchored or linked to any wider or narrower elements. However, this may just be a warning and not a blocking error.
The ESMA manual specifies that it is not necessary to anchor an extension if the extension element is a subtotal where all elements leading up to the subtotal are expressed as either standard elements or anchored extensions.
As long as the element in question is a subtotal with no extra financial information, the warning can be disregarded.