When I ran the below command
C:\Users\ASDF>elasticdump --input=http://username:pwd@domainname/indexnameone/ --output=http://username:pwd@domainnameone/indexnametwo --type=data
The error is
BAD_REQUEST: {"error":{"root_cause":[{"type":"action_request_validation_exception","reason":"Validation Failed: 1: type is missing;2: type is missing;
The document types were removed in the 5.x-7.x timeframe. So you are trying to index from the version of elasticearch that doesn't support types into the version where types are mandatory. Try specifying type on your target index:
elasticdump --input=http://username:pwd@domainname/indexnameone/ --output=http://username:pwd@domainnameone/indexnametwo/typenametwo --type=data