Login to your CoinGate account, go to API > Apps, and click on "+ New App". Fill out the form: enter a title, whitelist IPs if needed, your integration website, and choose an invoice expiration time and acceptable underpayment threshold if desired. Click "Submit". Copy-paste the displayed Access Token to your API integration code or module configuration window (it is only showed once for security purposes).
Please create different API credentials for each website where you are using CoinGate services.
Please note that if you wish to use Test Mode, you have to create an account on the sandbox environment and get API credentials there. API credentials generated on coingate.com will only work for Live Mode (production).