QuickBooks decided to end OAuth 1.0 support for all their apps by the end of January 2020. This was done for security reasons and you can read more information about the OAuth 1.0 to OAuth 2.0 migration efforts on the QuickBooks API documentation pages.
STEP 1 - Developer Portal
Navigate to https://developer.intuit.com/ and click on Sign In at the top right-hand side. You will see the login screen below.
STEP 2 - Login
Use the same login and password as you would when accessing your LIVE QuickBooks account.
STEP 3 - Create a new app
After a successful authentication click on My Apps at the top right and you will be redirected to the QuickBooks app dashboard. It should look similar to this:
STEP 4 - Create a new app
Click the blue-button at the top of the page with the following label: + Create an app
Click on QuickBooks Online and Payments box and fill out a form on the next image.
The app name can be anything, but we recommend you use a descriptive name (eg. Integration with mystore.com)
The scope should be set to Accounting.
Click on Create app button.
STEP 5 - App configuration
Terms of Service Links
EULA - a link to your site (technically this can be any URL since the only user of this app will be you.
Privacy policy URL - same as above. Noone besides you should be using this app.
Target industries for this app
Choose the industry for your business
Countries you accept connections from
Choose the country where your Magento is hosted.
We don't recommend using ALL as it will increase the security risk for this integration app.
Scope of the API
Should be set to Accounting.
Click Save.
STEP 6 - Keys and OAuth
Keys
This is where you will get the Client ID and Client Secret
You will need to populate these in Magento Admin
Redirect URIs
Click on Add URI
Copy-paste the callback URI from the Magento (see the TNW QuickBooks > General configuration page)
App URLs
Host Domain - is your website (eg. mystore.com)
Launch URL: https://powersync.biz/integrations-magento2-quickbooks
Disconnect URL: https://powersync.biz/quickbooks-disconnected
Click Save.
FINAL STEP
Go to Configuration: Connecting to QuickBooks to connect your app to Magento.