Go to BitMEX
Log in or create a new account on https://www.bitmex.com/.
Open account dashboard
Click the profile email on the top right corner, then click Account & Security.
Follow to API
Click "API keys" on the left side menu.
Name your key
When you have multiple APIs, a proper name helps to manage it.
You must select "Order" to use the key with 3Commas.
Enter 2FA code if required
Click "Create API Key"
Don't change other settings to avoid problems.