Builds ErgoPayRequest for SigUSD exchange

{
  "type": "object",
  "properties": {
    "address": {
      "type": "string"
    },
    "amount": {
      "type": "integer",
      "format": "int64"
    },
    "checkRate": {
      "type": "integer",
      "format": "int64"
    },
    "executionFee": {
      "type": "integer",
      "format": "int64"
    }
  },
  "required": [
    "address",
    "amount"
  ],
  "additionalProperties": false
}