Diagnosis
The quick-connect collar on the spray gun is either not being pulled back fully, or there’s debris or damage on the hose connector’s ball bearings.
How to Fix It
Pull the quick-connect collar on the gun all the way back toward the trigger. Firmly push the hose connector in until you hear/feel a definitive click. Release the collar.
If That Didn't Work
Disconnect and inspect both ends. Look for dirt or sand in the gun’s socket. Check that the small ball bearings on the hose connector move freely. Clean with a toothpick and light oil if stuck.
Heads Up
Never force it. The plastic threads on the gun can strip. Ensure you’re using the OEM hose or a compatible replacement; aftermarket fittings sometimes have slightly different tolerances.