Error when convert caffe eltwise layer

Good day

I have error when trying to convert with coremltools eltwise layer with coeffs in eltwise_param section:

layer {
  name: "eltwout"
  type: "Eltwise"
  bottom: "ch31"
  bottom: "poolout"
  top: "diff"
  eltwise_param {
  operation: SUM
  coeff: 1
  coeff: -1
  }
}

RuntimeError: Unsupported parameter 'coeff' in caffe layer 'eltwout' of type 'Elementwise'.

Any ideas?

Thanks!