RunPipeline is calling 5.1 preview API?

hi,
Thank you for writing this API. I'm trying to write a terraform provider to call this API to run my pipeline. I have written my version 1 code (new Go learner) and then I realize your RunPipeline function is calling Azure devops API 5.1 preview ? while 6.0 is available?
Here is your code to show you are pointing to 5.1-preview.
resp, err := client.Client.Send(ctx, http.MethodPost, locationId, "5.1-preview.1", routeValues, queryParams, bytes.NewReader(body), "application/json", "application/json", nil)

I still haven't get my code working, but I'm not sure whether I should continue to develop my code which bases on 5.1 preview API calling.

I'm currently stuck at Pipeline calling and not able to find RefName.
It basically located pipeline base on PipelineID but not able to take RefName as parameter and always refer to basic master branch instead of other branches.
I have tried both "refs/heads/xxxbranchName" and "xxxbranchName", not effect.

since it's using 5.1 preview API, I can't find document from Microsoft to details explain what API look like.

Can you upgrade the RunPipeline to API 6.0 at least?

Many thanks.

Locate the RunPipeline entry point and inspect its request construction, especially the 5.1-preview version and RefName handling. Compare those parameters with the Azure DevOps 6.0 API documentation, then verify that the requested version and branch reference are passed correctly before considering the issue done.