[Android Central Question]

Its a new phone but we've used it for 6 months

[Rukbat]

It suddenly started asking for a password? Then someone may have gotten it for a few minutes and added a password on the lock screen. If that's what happened, a little (metaphorical) "arm-twisting" might convince the person to tell you what the password is. (There's no way to "bypass" or "get around" it.

It's been asking for a password since you got it? Then it wasn't a new phone. In that case, although you should have returned it immediately, I'd still talk to wherever I bought it.

[Mooncatt]

It suddenly started asking for a password? Then someone may have gotten it for a few minutes and added a password on the lock screen. If that's what happened, a little (metaphorical) "arm-twisting" might convince the person to tell you what the password is. (There's no way to "bypass" or "get around" it.

This may be an exception. If the OP was logged in to their Google account on the phone, then there is the nuclear option of factory resetting from the recovery menu. Factory reset protection would kick in, where the OP could enter their Google account info and gain access to the phone again. At that point, all passwords should be changed from another device in case spyware was installed while the phone was out of their control.

If they did buy this used, it is possible they never went through the setup process and didn't sign into their Google account. In that case, a reset wouldn't work. It also brings up concerns about this being a stolen phone and the prior owner remotely accessed it to lock it out. Of course this is just speculation on possibilities without knowing enough info to make a single suggestion.