shared_link_access_denied when trying to access a shared file using the v2 api (status 409)

info:  the dropbox folder is in another users' account; I can access the file in question via the browser, even when I am not logged in to dropbox myself, by supplying the link_password when prompted.

However, when I use the api v2 and supply my token and the link_password, I receive the shared_link_access_denied.

Here is the curl call, (without the identifying information) -- 

curl -vX POST \
https://content.dropboxapi.com/2/sharing/get_shared_link_file \
--header "Authorization: Bearer _MY_BEARER_TOKEN_" \
--header "Dropbox-API-Arg: { \"url\":\"_THE_FILEs_URL?dl=1\",  "link_password\":\"_MY_LINK_PASSWORD_\"}"

The error I receive:

< HTTP/1.1 409 shared_link_access_denied/
< Server: nginx
< Date: Wed, 25 Jul 2018 10:29:50 GMT
< Content-Type: application/json
< Transfer-Encoding: chunked
< Connection: keep-alive
< Content-Security-Policy: sandbox allow-forms allow-scripts
< X-Dropbox-Request-Id: 7e722bc37889b435a4336c0661f86577
< X-Robots-Tag: noindex, nofollow, noimageindex
<
* Connection #0 to host content.dropboxapi.com left intact
* Closing connection #0
{"error_summary": "shared_link_access_denied/", "error": {".tag": "shared_link_access_denied"}}

Any suggestions, please?