Fix Lightspeed Kounta OAuth Connection in Google Apps Script — 90% Done, One Fix Needed

Fix Lightspeed Kounta OAuth Connection in Google Apps Script — 90% Done, One Fix Needed WHAT'S ALREADY BUILT I have a working Google Apps Script project (owned by my Google account) that connects to Tanda and Xero successfully. The project includes: OAuth2 library already installed All sheet tabs created (Dashboard, Daily, Weekly, Monthly, COGS_Tracker, RAW_Sales, RAW_Wages, RAW_COGS, Targets, Email_Log) Kounta config already structured in Code.gs with KOUNTA_CLIENT_ID, KOUNTA_CLIENT_SECRET, and KOUNTA_COMPANY_ID Lightspeed developer app already registered with Client ID: EkHz7V9KpiyHO8hU THE ONLY THING LEFT The Lightspeed Kounta OAuth connection is not completing. Kounta's authorization code expires in under 5 seconds — the token exchange must be handled instantly and automatically server-side. Manual copy-paste flows do not work. Lightspeed support confirmed: "the response actually needs to be near instant; it was designed with automation in mind." WHAT I NEED The connection completes automatically when I click Allow on the Kounta authorization page The access token is stored securely in Script Properties Sales data begins pulling from the Kounta API into the RAW_Sales sheet Access via Google share only — no credentials shared. PLEASE ONLY APPLY IF You have worked with Google Apps Script OAuth2 flows before You can explain in your proposal exactly how you would handle the sub-5-second token exchange requirement Applications that do not address the token expiry issue will not be considered.