Login to your Salesforce homepage and click the cog in the top right corner, followed by setup on the menu that pops out

On the setup page, click Apps on the left menu, and then App Manager

On the Lightning Experience App Manager screen, click the “New Connected App” button in the top right.

Enter the following information into the New Connected App Screen

Connected App Name: Yay.com
API Name: yay
Contact Email: help@yay.com
Contact Phone: 0330 122 6000

Check the Enable OAuth Settings box under API (Enable Oauth Settings) header.

Enter the following callback URL: https://www.yay.com/oauth/salesforce

Add the following Scopes to the list on the right from the “Selected OAuth Scopes”

Manage user data via APIs (api)
Perform requests at any time (refresh_token, offline_access)

Make sure ‘Require Proof Key for Code Exchange (PKCE) Extension for Supported Authorization Flows’ option is unchecked.

Click the Save button at the top of the page.

Once you have saved the app, on the next screen click the Manage Consumer Details button.

Make a note of the Consumer Key and Consumer Secret as you need these to complete the Yay.com installation process

Return to the setup menu and then App Manager from the first step. Click the dropdown arrow on the right for the new connected app just created, on the popup menu that appears click Manage

Click the Edit Policies button

Ensure the Refresh Token Policy is configured to Refresh token is valid until revoked