<p>Updates the parameter values for stack instances for the specified accounts, within the specified Amazon Web Services Regions. A stack instance refers to a stack in a specific account and Region.</p> <p>You can only update stack instances in Amazon Web Services Regions and accounts where they already exist; to create additional stack instances, use <a href="https://docs.aws.amazon.com/AWSCloudFormation/latest/APIReference/API_CreateStackInstances.html">CreateStackInstances</a>.</p> <p>During stack set updates, any parameters overridden for a stack instance aren't updated, but retain their overridden value.</p> <p>You can only update the parameter <i>values</i> that are specified in the stack set; to add or delete a parameter itself, use <a href="https://docs.aws.amazon.com/AWSCloudFormation/latest/APIReference/API_UpdateStackSet.html">UpdateStackSet</a> to update the stack set template. If you add a parameter to a template, before you can override the parameter value specified in the stack set you must first use <a href="https://docs.aws.amazon.com/AWSCloudFormation/latest/APIReference/API_UpdateStackSet.html">UpdateStackSet</a> to update all stack instances with the updated template and parameter value specified in the stack set. Once a stack instance has been updated with the new parameter, you can then override the parameter value using <code>UpdateStackInstances</code>.</p>

{
  "success": true,
  "data": {
    "id": "abc123",
    "created_at": "2025-01-01T00:00:00Z"
  }
}

{
  "success": false,
  "error": {
    "code": "VALIDATION_ERROR",
    "message": "Invalid request parameters"
  }
}