How to pass variable to REST API that is defined in Environment for a yaml pipeline and how to get the REST API to translate the variable - api

Question

In Azurce DevOPS I have a REST API defined in Environment and I have a yaml pipline that sets a variable. I want to pass this variable to the REST API but it does not work. I can get it to work fine in a Release Pipeline.
The REST API is used as a gate in Environment.
This is the URL and Parameters in the REST API servicenowchecker/api/ServiceNow/GetServiceNowChangeStatus/$(PipelineChangeNumber)?onlyDate=true and my problem is to get the content of $(PipelineChangeNumber) to work. I cannot fin out how it has to be written in URL and Parameters section
my yaml pipeline looks like this - can someone please help me out - thanks
name: Test_serviceNowCheker-$(Date:yyyyMMdd)$(Rev:.r)
trigger: none
variables:
name: PipelineChangeNumber
value: CHG0070534
stages:
stage: Stage1
jobs:
deployment:
pool:
name: dotNET
environment:
name: P1_Urgent_CRB_Environment
job: Say_Hello
pool:
name: dotNEt
steps:
task: PowerShell#2
displayName: Hello from stage1
inputs:
targetType: 'inline'
script:
write-host "Hello from stage 1";
task: PowerShell#2
displayName: Set Outputvar OutPutCase
inputs:
targetType: 'inline'
script: Write-Host "##vso[task.setvariable variable=ChangeNumber;isoutput=true]CHG0070534";
name: OutPutCase
powershell: |
write-host "OutPutCase.ChangeNumber = $(OutPutCase.ChangeNumber)";
write-host "PipelineChangeNumber = $(PipelineChangeNumber)";
stage: Stage2
dependsOn: Stage1
variables:
Stage2_ChangeNumber: $[ stageDependencies.Stage1.Say_Hello.outputs['OutPutCase.ChangeNumber'] ]
jobs:
deployment:
pool:
name: DotNet
environment:
name: P1_Urgent
job: Say_Hello_again
pool:
name: DotNet
steps:
task: PowerShell#2
displayName: Hello from stage2
inputs:
targetType: 'inline'
script:
write-host "Hello from stage 2";
write-host "Stage2_ChangeNumber = $(Stage2_ChangeNumber)";
write-host "PipelineChangeNumber = $(PipelineChangeNumber)";
I have tried to write the as $(PipelineChangeNumber) and $[ $(PipelineChangeNumber) ] then the REST API does not work at all.
When it is written as $[ $PipelineChangeNumber ] the REST API starts up but is sending https://XXXXXX-xx/servicenowchecker/api/ServiceNow/GetServiceNowChangeStatus/$[ $PipelineChangeNumber ]?onlyDate=true and the ¤PipelineChangeNumber is null.