->relationship('customer') 

 ->relationship('customer') 

Tabs::make('Tabs')
    ->tabs([
        Tabs\Tab::make('customer')
            ->schema([
                // ...
            ]),
        Tabs\Tab::make('Employee')
            ->schema([
                // ...
            ]),
    ])

Tabs::make('Tabs')
    ->tabs([
        Tabs\Tab::make('customer')
            ->schema([
                // ...
            ]),
        Tabs\Tab::make('Employee')
            ->schema([
                // ...
            ]),
    ])