You can remove the link between records by adding a nested element with the attribute action="delete" to the import. The procedure is generic; the example below uses a price level assigned to a price list item.
Request
<winstrom version="1.0">
<cenik>
<id>133</id>
<cenHladiny>
<cenova-uroven action="delete">
<id>6</id>
</cenova-uroven>
</cenHladiny>
</cenik>
</winstrom>
The parent record is identified by its usual identifier, and inside the relation you specify only the record that should be detached. The response shows this as an update of the parent record (updated), not as a deletion.
How to find out what is linked
GET /c/{firma}/cenik/133.xml?relations=cenHladiny&detail=custom:kod,cenHladiny(id)
💡 The same approach applies to any other relation — you just need to know its name. The list of relations for a given record type is available at /c/{firma}/{evidence}/relations.xml.
ℹ️ Only the link is removed, not the records themselves — both the price level and the price list item are preserved. For deleting entire records, see the article The difference between action=delete and the DELETE method.