DIAGNOSIS This is an accessory issue. The drinking lids are separate components from the blending cup and blade assembly.
FIX Replacement lids are available from the manufacturer or authorized parts sellers. You need the lid specific to your cup size: 17oz or 23oz. The lid is a two-piece assembly: a flat sealing lid and a sip-top cover. Ensure you order the correct size.
IF THAT DIDN'T WORK Generic replacement lids from other brands are unlikely to fit due to specific thread patterns and sealing designs unique to KOIOS cups.
HEADS UP Do not use the blending cup as a travel cup without a secure lid. The blade assembly is not leak-proof for transportation. Only the dedicated drinking lid provides a seal for carrying.