Azure DevOps REST API - How to update variable in Azure variable group?

I have an Azure pipeline for my test branch. I am trying to build a way to automatically increment the build number. The build number is saved in a variable build_number inside a group BUILD_NUMBER. I can read the build number, but I'm trying to update it from the pipeline so it can increment by 1 without having to manually update it myself.

Things Im not sure on:

• If this method of using System.AccessToken is working as intended
• The body I am supplying is correctly built (I included every field as per the docs but no change)
• If this is even the right way to be going about this

This is the powershell script I am running:

$authHeader = @{Authorization = "Bearer $(System.AccessToken)"}
          $body = @{
              description = "Build number"
              name = "BUILD_NUMBER_GROUP"
              providerData = @{
                  repository = @{
                      id = "some_id"
                  }
              }
              type = "Vsts"
              variables = @{
                  build_number = @{
                      isSecret = false
                      isReadOnly = false
                      value = "2" # this is programaticaly done in an earlier script
                  }
              }
              variableGroupProjectReferences = @(
                  @{
                      name = "BUILD_NUMBER_GROUP"
                      description = "Build number"
                      projectReference = @{
                          id = "100"  
                          name = "project_name"
                      }
                  }
              )
          } | ConvertTo-Json -Depth 10

          Invoke-RestMethod -Uri "https://dev.azure.com/{organisation}/{project}/_apis/distributedtask/variablegroups/100?api-version=7.2-preview.2" -Method Put -Body $body -Headers $authHeader -ContentType "application/json"
        displayName: "Increment build number"

I am unsure if this is along the right path, but I am getting this error:

Line |
  42 |  Invoke-RestMethod -Uri "https://dev.azure.com/{organisation}/{project} …
     |  ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
     |  {   "$id": "1",   "innerException": null,   "message": "Value cannot be
     | null.\r\nParameter name: variableGroupParameters",   "typeName":
     | "System.ArgumentNullException, mscorlib",   "typeKey":
     | "ArgumentNullException",   "errorCode": 0,   "eventId": 0 }

Based on your description, you need to use the Rest API: Variablegroups - Update to update the variable group in Azure Pipeline.

You can do the following changes in your PowerShell code:

1.You can simplify your Request Body to the following format:

$body = @{
      description = "Build number"
      name = "BUILD_NUMBER_GROUP"
      type = "Vsts"
      variables = @{
         build_number  = @{
             isSecret = "false"
             isReadOnly = "false"
             value = "2" 
           }
         }
 }| ConvertTo-Json -Depth 10

2.You can use the API version:api-version=5.1-preview.1

Rest API url:

PUT https://dev.azure.com/{organization}/{project}/_apis/distributedtask/variablegroups/{groupId}?api-version=5.1-preview.1

Full PowerShell script sample:

$authHeader = @{Authorization = "Bearer $(System.AccessToken)"}
 
$body = @{
      description = "Build number"
      name = "BUILD_NUMBER_GROUP"
      type = "Vsts"
      variables = @{
         build_number  = @{
             isSecret = "false"
             isReadOnly = "false"
             value = "2" 
           }
         }
 }| ConvertTo-Json -Depth 10


Invoke-RestMethod -Uri "https://dev.azure.com/{org}/{project}/_apis/distributedtask/variablegroups/100?api-version=5.1-preview.1" -Method Put -Body $body -Headers $authHeader -ContentType "application/json"

On the other hand, if you want to use the API version: api-version=7.2-preview.2

Rest API url:

PUT https://dev.azure.com/{organization}/_apis/distributedtask/variablegroups/{groupId}?api-version=7.2-preview.2

You can use the following Request Body:

$body = @{
      description = "Build number"
      name = "BUILD_NUMBER_GROUP"
      type = "Vsts"
      variables = @{
         build_number  = @{
             isSecret = "false"
             isReadOnly = "false"
             value = "2" 
           }
         }
      variableGroupProjectReferences = @(
               @{
                     name = "BUILD_NUMBER_GROUP"
                     description = "Build number"
                     projectReference = @{
                          id = "{ProjectID}"  
                          name = "{Projectname}"
                      }
                  }
              )
 }| ConvertTo-Json -Depth 10

Full PowerShell sample:

$authHeader = @{Authorization = "Bearer $(System.AccessToken)"}
 

$body = @{
      description = "Build number"
      name = "BUILD_NUMBER_GROUP"
      type = "Vsts"
      variables = @{
         build_number  = @{
             isSecret = "false"
             isReadOnly = "false"
             value = "2" 
           }
         }
      variableGroupProjectReferences = @(
               @{
                     name = "BUILD_NUMBER_GROUP"
                     description = "Build number"
                     projectReference = @{
                          id = "{ProjectID}"  
                          name = "{Projectname}"
                      }
                  }
              )
 }| ConvertTo-Json -Depth 10


Invoke-RestMethod -Uri "https://dev.azure.com/{orgname}/{projectname}/_apis/distributedtask/variablegroups/100?api-version=7.2-preview.2" -Method Put -Body $body -Headers $authHeader -ContentType "application/json"

You can get the Project ID with the Rest API: Projects - List