Diagnosis
The main folding latch bolt has worked loose, creating play in the stem. This is a high-stress point that requires periodic checking.
How to Fix It
Tighten the large vertical bolt inside the folding mechanism. Open the latch, locate the 8mm bolt head deep inside, and use a wrench to tighten it clockwise until the stem has zero side-to-side play when locked. Do not overtighten.
If That Didn't Work
The creak may be from the mating surfaces. Apply a small amount of bicycle grease or lithium grease to the contact points where the hook latch engages and where the stem meets the base.
Heads Up
Check this bolt every few weeks. A loose stem is a major safety hazard. If the bolt feels stripped or won't tighten, stop riding and contact Apollo for a replacement latch assembly.