Your 2FA secret key is not the code you get from the Authenticator app.
This is an activation code you get from LinkedIn once you turn on the 2FA. You can't access it again if you haven’t copied it in your notes when you got it. But worry not, you can reset it easily.
In case you lost your 2FA secret key on LinkedIn, you’ll need to disable 2FA and then turn it back on to get a new key. Be sure to save this new key in a secure location (e.g. your personal notes).
How to turn Two-Step Verification OFF in order to generate a new Secret Key?
Step 1: Access your LinkedIn account, find the 'Me' section, from the dropdown open 'Settings & Privacy'.
Step 2: Navigate to 'Sign in & Security' and hit the last option listed on the bottom named as 'Two-Step Verification'. Turn the option OFF by clicking in the button.
Step 3: LinkedIn can prompt you to either add your password in order to confirm this change or ask for a 6-digit code that will be sent to your email address.
In some cases, LinkedIn may ask for the both options in order to successfully turn your 2FA OFF, please proceed.
Once it's turned OFF, you can proceed with the article guidance linked in the text below.
Access and follow the instructions explained on the article titled How to activate the Infinite Login on HeyReach for the first time? in order to successfully set the Two-Step Verification and generate a new secret key that you can use for the Infinite login.