Error: Payload encoding error: Invalid type to construct an Amount

The payload creation for this json throws "Invalid type to construct an Amount" error. What is the format for Amount?

  user_token: '69002d91-8692-4ab2-8e7f-51d0a7d36082',
  TransactionType: 'NFTokenCreateOffer',
  txjson: {
    TransactionType: 'NFTokenCreateOffer',
    Account: 'rBaw9YZND7cDF1f2jQVE1bDsSZY1szv7fs',
    NFTokenID: '00080000C924488438D936EC938CCBD9D20F52AD732DF98B44B17C9E00000003',
    Amount: 100000000,
    Flags: 1,
    Destination: 'rKLYHZgkP3afTaBh9DyZZkq3B9n3wu9nyS',
    Owner: 'rKLYHZgkP3afTaBh9DyZZkq3B9n3wu9nyS'
  },
  options: {
    submit: true,
    multisign: false,
    expire: 15,
    return_url: 'http://localhost:3001'
  }
}```

[image.png](https://postimg.cc/tsY0mktX)