My Web-app(Gen-AI Q&A bot with RAG+Agent) launched in Azure-VM need an integration with SharePoint-Sites to fetch documents, for indexing and source reference. Tried through Entra-app registration(Sites.selected, User.Read). Getting Authentication issue.

Question

My Web-app(Gen-AI Q&A bot with RAG+Agent) launched in Azure-VM need an integration with SharePoint-(Sites, drives, lists, etc) to fetch documents for two purpose. One is for indexing of the document and other is referring back to source-document post Q&A answer generation . I have tried through Microsoft Entra-app registration with permissions "Sites.selected, User.Read".
Getting Authentication issue. I am able to read the list of folders but could not download them. When I am using my access token( taken from Microsoft graph explorer, where I have logged in using my credentials), I am able to download the documents.