Do you mean the password for the WiFi? It should be on the modem itself on the barcode or you should have received a fridge magnet with the login details.
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We just need a little more info @Hayat
Is this a brand new connection or an established service? If it's the same issue described by the OP, it could be a number of things.
Which lights are lit up one the modem? Other than a lit up WiFi light, we're looking for a solid green internet & DSL/Fibre (depending on the NBN technology type).
Do you have an NBN connection box (NTD) as part of your hardware setup? If so, you can try plugging in a desktop or laptop directly into the UNI-D port. That'll allow you to determine if the Optus supplied modem is the culprit.
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