MicroTube instructs you, in the Settings, to visit https://developers.google.com/youtube/registering_an_application
On that page you'll see that step 1 is to open https://console.cloud.google.com/apis/credentials, so let's go there directly.
Log in (if you weren’t already)
You’ll see a resource selector in the top left corner:
Click it to get the popup where you can create a new project:
Name your new project Microtube.
After you've created the project, you'll see an notification:
Click the Select Project link to directly go to your new project.
Go to Audience
Click Get started and follow the self-explanatory steps.
(The App name is MicroTube, Audience is External)
Add your own email address as test user.
Next, in the top bar search for YouTube, select the YouTube Data API v3
and click ENABLE
In the left menu, click Credentials and then at the top, click + Create credentials
And choose the Oauth client ID
Follow the steps.
(Application type = Desktop app)
Use the shown Client ID and Client secret in the MicroTube app on your phone.
Make sure that whatever you're using to copy the Client ID, doesn't turn it into a URL by adding 'Https://' to it.
MicroTube will open your browser where you'll log into Google and allow MicroTube the requested access. When you're at a blank page at http://127.0.0.1:1965, you can close the browser.
You’ll see the button in MicroTube now says Logout from YouTube.
Likes and dislikes in MicroTube will now be sent to YouTube and in the subscriptions section (in the pull down menu) you can import you subscriptions from YouTube. This wil copy your subscriptions and from now on new videos of those channels will appear in MicroTube. Subscribing/unsubscribing in MicroTube will not affect your subscriptions in YouTube.