Britax toddler seat - suitable for non-car use (Newcastle Central NE1)

Britax semi-universal model 9-25 kg. Signage shown in photos. Reasonable condition, slight marks but no damage. We got this second hand to use for a visit by family with toddler and it worked absolutely fine. It has a strong prop-up leg to allow it to be used on the floor, with a child strapped in. However, we have mislaid the strap which attaches it to a car seat, so it cannot be used for that purpose (unless the strap required for this model is purchased). The seat has instructions for use plus a QR code.