PBI Data send through HTTP to be filled into Word Template

Hi WonderfulK 
Thank you for contacting the Microsoft Fabric community forum.

The issue is not related to the DAX or JSON logic, but to platform limitations with Power BI custom visuals. HTML visuals run in a sandboxed and security-restricted environment, which makes direct authenticated HTTP POST requests to Power Automate HTTP triggers unreliable and unsupported.
 

Although the Power Automate HTTP trigger URL contains authentication parameters, browser security restrictions and Power BI’s controlled authentication model can prevent the required headers or signatures from being passed correctly, resulting in HTTP 400/authentication-related errors.
 
As recommended by lbendlin , use the native Power Automate visual within Power BI instead of the HTML visual with an HTTP trigger. This is the supported integration method and automatically handles authentication and report filter context for scenarios such as generating Word documents from Power BI data

Here are some references:
The authentication API in Power BI custom visuals - Power BI | Microsoft Learn
Create a Power Automate visual for Power BI - Power BI | Microsoft Learn
 
If you have any further questions, feel free to reach out and we'll be glad to assist.
 
Regards,

Microsoft Fabric Community Support Team.
 

Yes i think i got my answer much appreciated