Facing issue in R Shiny app for downloading email attachments.

So I am a data analyst and recently I am working on automating the task of downloading email attachments (po, grn etc pdfs). I am using R Shiny for it, where I have created an app like interface.

I am using the API for accessing Gmail. I have enabled the API, correctly configured the OAuth consent screen, defined all the scopes in the code, my authentication is also successfully happening by going on the web but still my code is not able to fetch any mail data. I am getting the forbidden:http (403).