No internet access: LOS (Loss of Signal) LED flashing.
A Loss of Signal (LOS) alarm indicates a physical link problem, in this case, a connection to the fiber converter. A LOS alarm can originate from a break in the fiber optic cable, problems with the converter, or a splice box. The solution usually involves contacting the Internet provider.
The fiber used is single-mode, and to see any signal, the cell phone camera must have an infrared filter that lets something through. On iPhone devices, at least the 11 model, the front camera allows you to partially see the light from the fiber (it must be captured at distances greater than 10cm to avoid damaging the camera sensor). Therefore, it is possible to see the presence of light, but it is not recommended with a phone, but rather with a Power Meter or devices for this purpose.
In short, the LOS LED indicates a physical problem, which is the absence of light in the fiber, requiring intervention from the Internet provider.