need help on the endpoint for fetching from my own server API from within a Keroku app in production

my stack overflow post is here

https://stackoverflow.com/questions/62906227/need-help-on-the-url-for-fetching-from-within-an-app-on-heroku

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as of now, I have a fetch request in development mode to query the api exposed at localhost:3000/send-email.

axios.post('http://localhost:3000/send-email', data) .then(() => { setSent(true) }) .then(() => { resetForm() }) .catch((err)=> { console.log('Message not sent', err) }) 

When I deploy to heroku, I am no longer wanting to point to localhost. What do I change it to? would it be just pointing to my own domain name like this?

axios.post(`http://www.example.com/send-email`, data) 

I can't seem to find the right thing to search for for this step.