Getting authorization for access token denied

Am in Pakistan and client in Australia, I created an addon for private use in her account with name: integration for gohighlevel to serviceM8

Added the addon.manifest.json, wrote the backend to handle requests and deployed it on heroku. I have made sure app I'd and Secrets are same everywhere( manifest, server.js, addon page) also asked client to open the installation url with her account as the addon is on her account so that I can get the access token in my heroku logs. But she got access denied page with url https://go.servicem8.com/access_denied?strFrom=%2Fapi_oauth%2Fauthorize%3Fclient_id%3D105007%26redirect_uri%3Dhttps%253A%252F%252Fintegwithghl-0125ea6b2dc5.herokuapp.com%252Foauth%252Fcallback%26response_type%3Dcode%26scope%3Dstaff%2520job%2520client%2520invoice

Heroku logs show status 302 for activation url when she opens the link, and when I check the callback url manually it says missing authorization code.

What's the issue guys plz help me resolve it.