Error in callback when unregistered client requests the authorization GET route

[jankapunkt]

I20190830-14:03:45.614(2)? Exception in callback of async function: Error: Can't set headers after they are sent.
I20190830-14:03:45.614(2)?     at validateHeader (_http_outgoing.js:491:11)
I20190830-14:03:45.614(2)?     at ServerResponse.setHeader (_http_outgoing.js:498:3)
I20190830-14:03:45.614(2)?     at ServerResponse.setWriteHeadHeaders (/Users/admin/.meteor/packages/webapp/.1.7.4.11um7dv.19c5h++os+web.browser+web.browser.legacy+web.cordova/npm/node_modules/on-headers/index.js:82:19)
I20190830-14:03:45.614(2)?     at ServerResponse.writeHead (/Users/admin/.meteor/packages/webapp/.1.7.4.11um7dv.19c5h++os+web.browser+web.browser.legacy+web.cordova/npm/node_modules/on-headers/index.js:41:36)
I20190830-14:03:45.614(2)?     at errorHandler (packages/leaonline:oauth2-server/error.js:3:7)
I20190830-14:03:45.614(2)?     at packages/leaonline:oauth2-server/oauth.js:155:11
I20190830-14:03:45.615(2)?     at runWithEnvironment (packages/meteor.js:1286:24)
I20190830-14:03:45.615(2)?     at packages/meteor.js:1299:14
I20190830-14:03:45.615(2)?     at packages/leaonline:oauth2-server/webapp.js:11:15
I20190830-14:03:45.615(2)?     at /Users/admin/.meteor/packages/promise/.0.11.2.hy69oz.ytuae++os+web.browser+web.browser.legacy+web.cordova/npm/node_modules/meteor-promise/fiber_pool.js:43:40
W20190830-14:03:45.615(2)? (STDERR) [ERROR] 500 - unauthorized_client - This client is not authorized to use this service