AutoNAT not connecting: what to check
A short checklist for when remote viewing on a Sibell recorder stops working, in the order worth trying.
Read the NAT status on the recorder
Start at Start → Settings → Network → NAT and look at the status, not the checkbox. Enabled with a status that never reaches connected means the recorder cannot reach the AutoNAT server, and no amount of retrying in a browser or app will change that. If the status is connected and you still cannot see the device remotely, the problem is on the client side instead.
Check the recorder's route out
Go to Start → Settings → Network → TCP/IP. A recorder can have a valid local IP address and still have no internet: the usual culprits are a missing or wrong gateway, or a DNS server that is not reachable. If the recorder is set to obtain its address automatically, confirm DHCP is actually enabled on the router. On units with built-in PoE ports, the internal camera network is a separate interface and is not the one that needs internet access.
Try the other web address
Both www.autonat.com and www.autonat.us resolve, and Sibell documentation notes that different regions may use different visit addresses. Trying the alternate address takes seconds and occasionally is the whole answer.
Separate the network problem from the account problem
Test the app on the same local network as the recorder, connecting by IP address. If that works, the recorder and your credentials are fine and the fault is the internet path or the NAT setting. If a device appears on one phone but not on another signed into the same account, that is the NAT2.0 and security code step rather than a connectivity fault.
Then the boring causes
A changed recorder password that was never updated in the app. A router replaced or reconfigured since the system was installed, dropping the recorder's static address or DHCP reservation. An ISP change of router that blocked outbound connections. Work through these before assuming a hardware fault — a recorder that records locally but will not connect remotely is almost always a network problem, not a failing unit.
Menu paths follow the Sibell recorder documentation. Wording and available options vary by model and firmware version — check the manual for your exact product, and confirm anything ambiguous with the authorized reseller before changing settings on a live system.