Add metadata to existing coupon

[pbmolini]

Hello, I try with the following and I get no errors

@wc_api_client.put("coupons/42", { meta_data: [{ key: "email", value: "email@example.com" }] })

but then nothing changes on the Coupon

@wc_api_client.get("coupons/42")['meta_data']
=> nil

What am I doing wrong?