I'm getting "MongoServerError: Invalid $project :: caused by :: Unrecognized parameter to $cond: $if" for this code. Whats wrong with it and how do i fix it ?

       {
          $project: {
            _id: 1,
            date: 1,
            slot: 1,
            franchiseId: 1,
            status: 1,
            order: {
              $cond: {
                $if: { $gt: ['$carspa', null] },
                $then: {
                  price: '$carspa.price',
                  mode: '$carspa.mode',
                  address: '$carspa.address',
                  addOn: '$carspa.addOn',
                  service: '$carspa_service.name'
                },
                $else: {
                  $if: { $gt: ['$mechanical', null] },
                  $then: {
                   price: '$mechanical.price',
                   mode: '$mechanical.mode',
                   address: '$mechanical.address',
                   addOn: '$mechanical.addOn',
                   service: '$mechanical_service.name'
                  },
                  $else: {
                    price: '$quickhelp.price',
                    mode: '$quickhelp.mode',
                    address: '$quickhelp.address',
                    addOn: '$quickhelp.addOn',
                    service: '$quickhelp_service.name'
                  }
                },
              },
            },
          }
        }