Open External Link When click on custom button in job board

Hi Support,

I am developing an SDK Add-on for my client. The requirement is to have a "Download Attachments" button for each job. When clicked, all attachments in the job notes should be downloaded to the local computer in a ZIP file.

I have written the code in PHP that accepts a job UUID and downloads all the attachments for that job. The script works perfectly.
I have successfully created the "Download Attachments" button using the manifest.json file.
Problem: I am unable to trigger my PHP external URL when the button is clicked. My goal is for the button to open a new tab with a URL like "https://www.domain.com/download_attachment.php?uuid=xxxxxxxxxxxx".

Note: I have already posted this query on the developer discussion portal. I received a response with the link https://developer.servicem8.com/docs/your-first-add-on, but it did not resolve my issue with hitting the external link.

I would be very grateful for your assistance in resolving this matter.