I returned the product immediately after purchase, I was not happy with it

Check by hand to see if any air is escaping, I have the same problem, if necessary tighten the screws and check the seals in the head. For the moment, it is working reasonably well again.

Test 1: Reinsert the bottle, make sure the thread runs smoothly and screw tightly.
Attempt 2: the fizzer may be blocked or clogged (sweet drinks fizzy). Rinse for a long time and keep rinsing and rinsing.
If none of this helps -> service