A cost approval is not a guarantee for all costs. It applies to the service described and usually up to a certain amount. If the transport changes — different type of transport, different destination, additional waiting time — the insurer should be informed. So read the approval carefully and keep it together with the invoice.
With basic insurance, there is normally no advance approval for transport; the statutory rules apply there, with 50 per cent and at most CHF 500 per year.
If there is a discrepancy despite the approval, for example because the actual costs turn out higher, a calm conversation with the insurer is worthwhile. A short explanation from the transport company can often clarify why, for example, waiting time or a different route was necessary.