How is the fibre patch cable supposed to be plugged in?

The fibre-optic patch cable has a blue and a green end. The two connectors are different from each other even if they look similar by the naked eye. You have to patch the connectors as follows:

AVM FRITZ!Box 5490
SC/PC (blue) –> into the SC slot of your FRITZ!Box
LC/APC (green) –> into the fibre-optic socket (OTO)

MikroTik RB2011UiAS-2HnD-IN Router
LC/PC (blue) –> into the optics of your MikroTik router
LC/APC (green) –> into the fibre-optic socket (OTO)

TP-Link MC220L Media-Konverter
LC/PC (blue) –> into the optics of your media converter
LC/APC (green) –> into the fibre-optic socket (OTO)

Please take care that you do not touch the sensitive ends of the fibre-optic cable after removing the protection caps. Insert the fibre-optic patch cable until you hear a click. If you do not patch the fibre-optic patch cable properly, this can cause a malfunction.

Removing the fibre-optic patch cable
Press the small lever slightly together and pull the fibre-optic cable carefully out of the slot. Put the protection caps immediately on the end of the cable.