Test it empty first
Close the case with nothing inside, press every edge until it clicks, and hold it underwater in a sink or bucket for 30 minutes. Dry it, open it, and check for any droplets. No water inside means the seal is good.
Take off the old screen protector
The case has its own protector built in. A second layer underneath pushes the front away from the frame and can break the seal. Peel off any existing glass before fitting.
Fit, then re-teach the fingerprint
Snap the phone in, check each edge again, and then go to Settings to register your fingerprint again. The reader is now looking through one more layer, and it needs a fresh scan.
After salt or chlorine
Rinse the closed case in fresh water, dry it, and only then open it. Salt left in the seal can wear it down over time. Store the case open so the gasket can rest.
