If you have already connected your Coupon Reach account to your GoHighlevel account before through the CouponReach App, the connection only stays active if you don't log out and if you keep using the same browser.
Additionally, if your browser's cache is reset, this may lead to disconnecting the API keys as well.
At the moment, there is no permanent way of storing the Coupon Reach API key in GHL to keep the connection active.