An integration connects FieldForms to a third-party service (an SMS gateway, a telephony provider, etc.). Open Integrations and select the one you need to configure it.
When you save an API key or secret, the field will show blank the next time you open the page — that's expected, and means "a value is already saved," not that it was lost. Leaving the field blank and saving again keeps the existing credential; it's never accidentally wiped by resaving the form. Only type a new value when you actually want to replace it.