The first thing to work out is whether the inverter genuinely isn't producing, or whether it's producing fine but the monitoring app just isn't getting the data. These look identical in the app but have completely different causes. A surprisingly common culprit is the WiFi data stick (dongle) losing its connection, which makes the app report zero generation even though the panels are working away normally.
To tell them apart, scan for local WiFi networks near the inverter — many inverters broadcast their own network (something like "Solis_xxxx" or a similar prefix). If you can see it, the inverter itself likely has power and it's just a data/upload issue, often fixable by reconnecting the dongle to your home WiFi. If there's genuinely no power at the inverter, check the obvious things: a tripped fuse or breaker on the inverter circuit, or a tripped RCBO. A tripped fuse is a common and easy explanation for a sudden total loss of generation on an otherwise sunny day.
If the fuse keeps tripping, or there's no power and no fault you can find, that's one to put back to your installer — repeated tripping can indicate an underlying electrical fault rather than a one-off. Cold weather affecting the WiFi dongle, firmware glitches, and loose connections are all common causes, so start with "is it really off, or just offline?" before assuming the worst.