I got same problem. So I looked into the axios document. I found it. you can do it like this. this is easiest way. and super simple.
https://www.npmjs.com/package/axios#using-applicationx-www-form-urlencoded-format
var params = new URLSearchParams();
params.append('param1', 'value1');
params.append('param2', 'value2');
axios.post('/foo', params);
You can use .then,.catch.