request_headers = { "Content-Type" => "application/x-www-form-urlencoded" }
request_body = URI.encode_www_form(
  [
    ...
    [
      "device_id",
      Pact.term(
        generate: "3387FE91-453B-4237-B986-17F4F0DC0E13",
        matcher: /^[a-zA-Z0-9]{8}-[a-zA-Z0-9]{4}-[a-zA-Z0-9]{4}-[a-zA-Z0-9]{4}-[a-zA-Z0-9]{12}$/
      )
    ]
    ...
  ]
)

interaction_mock_domain = "<http://127.0.0.1:9292>"
interaction_mock_path = "/interactions"
interaction_mock_headers = { "X-Pact-Mock-Service" => true }
interaction_mock_body = {
  request: {
    method: request_method,
    path: request_path,
    headers: request_headers,
    body: request_body
  },
  response: {
    body: response_body
  }
}.to_json
RestClient::Request.execute(
  url: interaction_mock_domain + interaction_mock_path,
  method: :post,
  headers: interaction_mock_headers,
  payload: interaction_mock_body
)

...
* Expected "Pact::Term matcher: /^[a-zA-Z0-9]{8}-[a-zA-Z0-9]{4}-[a-zA-Z0-9]{4}-[a-zA-Z0-9]{4}-[a-zA-Z0-9]{12}$/ generate: \"3387FE91-453B-4237-B986-17F4F0DC0E13\"" but got "3387FE91-453B-4237-B986-17F4F0DC0E13" at $.body.device_id[0]
...

request_body = {
  ..
  "device_id" => Pact.term(
    generate: "3387FE91-453B-4237-B986-17F4F0DC0E13",
    matcher: /^[a-zA-Z0-9]{8}-[a-zA-Z0-9]{4}-[a-zA-Z0-9]{4}-[a-zA-Z0-9]{4}-[a-zA-Z0-9]{12}$/
  ),
  ..
}
interaction_mock_body = {
  request: {
    method: request_method,
    path: request_path,
    headers: request_headers,
    body: request_body
  },
  response: {
    status: 200,
    headers: response_headers,
    body: response_body
  }
}.to_json