Did you check the endpoint via your webbrowser ?
F12 console > Network and check the API call when doing EXPORT ?
/api/status should work
Your prefix seems to be different
What is your opensearch_dashboard.yml configuration ?
Yeah, I got the complete URL for export, _bulk_get and import API calls, from the F12.
However, still unable to import or export using curl, getting the same error 404. not found. 
Here is the error message.
< HTTP/1.1 404 Not Found
Hello @ThibaudF,
I am able to import the dashaboard and visualization using CURL command successfully.
Here is the command I have used to import it.
curl -X POST "localhost:5601:/api/saved_objects/_resolve_import_errors" -k -u admin -H "osd-xsrf: true" --form file=@dashabord.ndjson --form retries='[{"type":"visualization","id":"xxxxxxxxx","replaceReferences":[{"type":"index-pattern","from":"xxxxxxxxxx","to":"xxxxxxxxxx"}]}]'