Gitlab Draft-note API bug when posting multi-line comments

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Problem to solve

When using the GitLab Draft Notes API:  https://docs.gitlab.com/api/draft_notes/#create-a-draft-note, we are trying to post multi-line comments using the position  arguments. We followed this https://docs.gitlab.com/api/discussions/#parameters-for-multiline-comments to fill the parameters, however GitLab is throwing An error occurred: 400 (An error occurred: 400 ({"message":{"position":["must be a valid json schema"]}})) when we send old_line, new_line parameters in position[line_range][start]  argument.  

We are providing the correct line_code. If we remove the old_line and new_line parameters (which are optional), the multi-line comment works, but it doesn't show the comment line badge in the UI.
However, I was also facing issue with line_code field. As an example, I posted this multi-line comment through UI and inspected the network call. This is their line_range param:

{
  start: {
  line_code: "****************************************_33_34",
  type: "old",
  old_line: 33,
  new_line: null
  },
  end: {
  line_code: "****************************************_36_36",
  type: "new",
  old_line: null,
  new_line: 36
  }
}

The comments were applied from -33 to +36. Based on this, not sure how <old_line> and <new_line> are computed in the line_code: <SHA>_<old_line>_<new_line> as 33_34 for start, and 36_36 for end.

To summarize the issues that we are observing

1. If I send old_line and new_line params in line_range (we took this information from the network calls, so our request was exactly the same as the network call) GitLab throws ({"message":{"position":["must be a valid json schema"]}}))
2. The line_code format recommended in the doc does not matches what I'm seeing in the network calls while making multi-line comment from the UI. But if I use the same line_code from code, it does works. So not clear on the proper recommendation of line_code format.

Proposal

Could you please test this API and provide further documentation and examples on use or if there is a bug on Gitlab's side could get an estimate of the fix.