While using web browser, You will need to open the http://AMBARI_SERVER_HOST:8080 URL first in the browser then it will ask for username or password . One you are authenticated then you can open the previously mentioned URL. http://AMBARI_SERVER_HOST:8080/api/v1/clusters/c1/services
If you are using Curl or wget then you can simply use the following:
curl -u $USER:$PASS -i -H 'X-Requested-By: ambari' -X GET http://AMBARI_SERVER_HOST:8080/api/v1/clusters/c1/services
As mentioned by Namit, do be sure to follow the Prerequisite instructions under https://docs.hortonworks.com/HDPDocuments/HDP2/HDP-2.5.3/bk_data-movement-and-integration/content/ch... before reinstalling. If you encounter any issues with these instructions, please let me know.