哦，大约一个月后，我终于找到了解决方案.对于 GravityForm API 的身份验证，OAUTH 1.0 并不像您预期​​的那样稳定.相反，您***使用BASIC AUTHENTICATION".像这样:

Oh, after about a month, I finally reached a solution. For authentication of GravityForm APIs, OAUTH 1.0 is not as stable as you may expect. Instead, you'd better use "BASIC AUTHENTICATION" like this:

USERNAME = consumerKey
Password = consumerSecret

然后您可以使用以下解决方案:RestSharp HttpBasicAuthentication - 示例

Then you can use following solution: RestSharp HttpBasicAuthentication - example