Warranties are used in an insurance contract to limit the liability of the insurer under certain circumstances.
A warranty is a condition expressly stated in the policy which has to be literally complied with for validity of the contract. Warranty is not a separate document. It is part of the policy document.
If certain terms and conditions of the policy need to be changed at the time of issuance, it is done by setting out the amendments / changes through a document called endorsement.
A co-payment is a cost-sharing requirement under a health insurance policy that provides that the policyholder/insured will bear a specified percentage of the admissible claim amount. A co-payment does not reduce the Sum Insured.