How to conditionally fail requests based on request counts

Open Requestly and create a new Modify Response rule.

Choose the Dynamic JavaScript option to write custom logic for the response.

Use the following code to fail the first request and let others succeed:

Copyfunction modifyResponse(args) {
  const {
    method, url, response, responseType,
    requestHeaders, requestData, responseJSON
  } = args;

  // Get the current count or start from 0
  let count = $sharedState.count ?? 0;
  count++;
  $sharedState.count = count;

  // Succeed if it is not the first request
  if (count > 1) {
    return null;
  }

  // Allow all subsequent requests to succeed
  return response;
}