In the API section of the App service pane, update the CORS setting to * or "https://www.qnamaker.ai". If this doesn't resolve the issue, check for any organization-specific restrictions.
https://video2.skills-academy.com/en-us/azure/ai-services/qnamaker/troubleshooting#manage-service
https://stackoverflow.com/questions/58232066/any-one-aware-about-qna-maker-cors-settings