FTX API - Submit lending offer doesn't work

I try to lend my balances automatically But i get this response: {'success': False, 'error': 'Missing parameter coin', 'errorCode': 'parameter_missing'}

import json
import time
import hmac
from requests import Request, Session

API_KEY = 'MY KEY'
API_KEY_SECRET = 'MY SECRET'

data = json.dumps({
  "coin": "ETH",
  "size": 0.15,
  "rate": 88e-4
})

ts = int(time.time() * 1000)
request = Request('POST', 'https://ftx.com/api/spot_margin/offers', data=data)
prepared = request.prepare()
s = Session()
signature_payload = f'{ts}{prepared.method}{prepared.path_url}'
if prepared.body:
    signature_payload += prepared.body
signature_payload = signature_payload.encode()
signature = hmac.new(API_KEY_SECRET.encode(), signature_payload, 'sha256').hexdigest()

prepared.headers['FTX-KEY'] = API_KEY
prepared.headers['FTX-SIGN'] = signature
prepared.headers['FTX-TS'] = str(ts)
prepared.headers['FTX-SUBACCOUNT'] = 'MY SUBACCOUNT'

response = s.send(prepared)
data = response.json()
print(data)