Postman Approach Working with PDF Extract API, Having Trouble With R approach

I am getting 403 errors when I attempt to access the PDF Extract API using R (specifically the httr package).

The API works fine in Postman, and I have successfully used the following R code to generate a "Bearer" token:

r = POST(
  url = "https://ims-na1.adobelogin.com/ims/exchange/jwt/",
  body = list(
    client_id = {{Placeholder for client_id}},
    client_secret = {{Placeholder for client_secret}},
    jwt_token = {{Placeholder for jwt_token}}
  ),
  encode = "form"
)

access_token = content(r)$access_token
Authorization = paste("Bearer", access_token)

The "Bearer" token that I have generated using R works fine when I copy and paste it into Postman for posting a PDF file and getting the extracted JSON data. So far, so good.

But I get a 403 error if I try to use the same "Bearer" token (and my client_id) to get the same extracted JSON data into R using the following R code:

httr::GET(
  url = "https://cpf-ue1.adobe.io/ops/id/{{Placeholder for x-request-id}}",
  config = list(
    add_headers(
      Authorization = {{Placeholder for Bearer token}},
      "x-api-key" = {{Placeholder for client_id}}
    )
  ),
  verbose()
)

Has anyone else solved this problem, or is there any documentation for R users I may have missed? Thanks!