Parameters and key value pairs for VotingAPI
I solved it. The entity ID is the node id (nid) if you are voting on a node for example. eg for nid of 75, it is entity_id: 75. Other parameters are 'percent', 'points' or 'options' for vote type. And for tag it is 'vote' or whatever custom tag you created as a field.  The 'value' of course is the number you are voting. If you are using standard settings for 5star, you enter eg 20 (for 1 star), 40, 60, 80 or 100 (5 stars). The mandatory parameters are entity_id, tag and value. I've read the system can work out the other details, eg user id from the currently logged in user.

eg this format worked for me: let newVote = ["votes":[["value":100,"uid":32,"entity_id":1,"entity_type":"node","tag":"vote","value_type":"percent"]]]

see Votingapi REST server call internal server error - &#39;services exception: missing entity ID&#39;