Go to Coinbase Pro
Log in or create a new account on https://pro.coinbase.com/.
Follow to API
Click the profile name on the top right corner, then click API.
Click "+New API Key"
You must enable:
Note the passphrase
You need it to add Coinbase Pro to 3Commas.
Click "Create API Key"
Don't change other settings.
Add Coinbase Pro to 3Commas
Note the secret key. You can copy and paste it right away to 3Commas.
Check how to connect API to 3Commas.