Whenever I want to use kc.updateToken the post request fails with 400 because the form data refresh_token is "undefined":

kc.updateToken cannot access kc.refreshToken
https://github.com/keycloak/keycloak/blob/master/adapters/oidc/js/src/main/resources/keycloak.js#L651

Form Date of the POST request from the browser to keycloak looks like this:
grant_type=refresh_token&refresh_token=undefined&client_id=clientId
(notice the refresh_token=undefined)

console.log trace

[KEYCLOAK] Estimated time difference between browser and server is 1 seconds
index.js:16 --- After Init; Before Update ---
index.js:17 Access Token: eyJhbGciOiJSUzI1NiIsInR5cC<removed>ZxiNLT4gnf39P-zdpGRKCpg
index.js:18 ID Token: eyJhbGciOiJSUzI1NiIsInR5cCIgOi<removed>1KMpLCwFObm5nXntMaRnPrg
index.js:19 Refresh Token: eyJhbGciOiJIUzI1NiIsInR5c<removed>YNDM3tAWM6GA4oIoXqs-CAY
keycloak.js:1759 [KEYCLOAK] Refreshing token: token expired
keycloak.js:696 POST https://<url>/protocol/openid-connect/token 400
keycloak.js:1759 [KEYCLOAK] Failed to refresh token
index.js:28 --- updateToken().catch() ---
index.js:29 Access Token: undefined
index.js:30 ID Token: undefined
index.js:31 Refresh Token: undefined

code to reproduce

kc.init({ onLoad: 'check-sso', silentCheckSsoRedirectUri: window.location.origin + '/silent-check-sso.html', pkceMethod: 'S256', promiseType: 'native', enableLogging: true, }) .then((authenticated) => { if(authenticated) { console.log('--- After Init; Before Update ---') console.log('Access Token: ' + kc.token) console.log('ID Token: ' + kc.idToken) console.log('Refresh Token: ' + kc.refreshToken) kc.updateToken(5) .then(() => { console.log('--- updateToken().then() ---') console.log('Access Token: ' + kc.token) console.log('ID Token: ' + kc.idToken) console.log('Refresh Token: ' + kc.refreshToken) }) .catch(() => { console.log('--- updateToken().catch() ---') console.log('Access Token: ' + kc.token) console.log('ID Token: ' + kc.idToken) console.log('Refresh Token: ' + kc.refreshToken) }) } else { kc.login({ redirectUri: ${window.envConfig.WEB_BASE_URL}/dashboard }) } })

Any idea what I'm doing wrong?