Failed to copy data from sharepoint in azure data factory pipeline using copy job

Question

I tried to copy files from sharepoint shared document into data factory with OAUTH2 token, I have successfully get the access token by sending "POST" request to https://accounts.accesscontrol.windows.net/xxxxxx/tokens/OAuth/2. I set up a copy activity by sending "GET" request to sharepoint, putting the following statement as the "Additional headers".
@{concat('Authorization: Bearer ',activity('Get Token').output.access_token)}
I also received "Connection successful" in link service connection test, but the following error occurred after executing the copy activity.

I have checked that the permission "Sites.Read.All" has been granted to my registered application, does anyone run into the same problem?