You are not alone. The ZTE H3601 is a popular optical network terminal (ONT) and router combo, widely used for fiber-to-the-home (FTTH) connections. However, finding the correct default credentials can be frustrating because ISPs often customize them.
A hard reset wipes all custom settings and restores the factory default password (usually admin/admin or the sticker value). zte h3601 default password
After reset, try logging in with the or admin / admin . You are not alone