Install

On-premise

download using "witadmin" the workitem definition and add to the web layout extensions:

<Extension Id="capito.link-count-limiter-dev" />

then in the first page add

<ControlContribution Id="liran.link-count-limiter-dev.only-one-wit-observer">
  <Inputs>    
    <Input Id="WorkitemLinkType" Value="System.LinkTypes.Hierarchy-Reverse" />
    <Input Id="LinkCount" Value="1" />
    <Input Id="WorkitemType" Value="Product Backlog Item" />
    <Input Id="CustomErrorMessage" Value="You Must have a PBI parent" />
  </Inputs>
</ControlContribution>

Cloud

Open the Process template for an inherided template select the workitem to which the limit affects it

Add custom extension

Select the options tab to set the control inputs

Work Item Link Types for example:

• System.LinkTypes.Hierarchy-Reverse - Parent
• System.LinkTypes.Hierarchy-Forward - Child

Look at Link Types for more options