Insurance when renting gear is not included and is not compulsory, but recommended. It can be purchased for Europeans with the VDWS (https://cp.vdws.de/safetytool) or with the IKO for further nations (https://www.ikointl.com/kiter-membership). If you damage equipment, the damaged will need to be paid on the boat. Afterwards you will get the money back from your equipment insurance.