3rd party developer auth

Has anyone had issues with the api call to get a refresh token? I am following the format in the docs but it keeps giving me errors when trying to get a new refresh token. Any help would be great!

let sendToken = await fetch(https://public-api.shiphero.com/auth/refresh`, {
method: “POST”,
headers: {
“refresh_token”: “exampletoken”,
“Content-Type”: “application/json”

    }).then(response => response.json()).then(data => {
        .catch((err) => {

Not sure, I just tested with my refresh token and it went through. I do see that it looks like there is a single quote at the end of the urlimage