Many couriers exclude musical instruments from insurance cover in the small print (but still let you buy it)
The main reason I have promoted Eurosender here is that, despite a few issues here and there (as you’ll find with ANY courier or booking service) is that they specifically cover instruments with a third party insurer, as long as the instrument is in a hard case.
https://www.eurosender.com/en/terms-conditions
ERGO insurance is the company providing the cover.
Still, you only find out how good that is when something bad happens - but insurance always feels like that. I’d never ship an instrument without proper cover.