https://documentation.onesignal.com/docs/web-push-sdk-setup-http

Web.config

<appSettings>
    <add key="OneSignalSubDomain" value="smk-demo"/>
    <add key="OneSignalAppID" value="***-***-***-***-******"/>
    <add key="OneSignalREST" value="****"/>
    <add key="ExternalSite" value="http://hospitality.datainsighthub.com"/>
</appSettings>

View

@{ 
    string appId = System.Configuration.ConfigurationManager.AppSettings["OneSignalAppID"];
    string subdomainName = System.Configuration.ConfigurationManager.AppSettings["OneSignalSubDomain"];
}



<script src="https://cdn.onesignal.com/sdks/OneSignalSDK.js" async='async'></script>
<script>
    var OneSignal = window.OneSignal || [];
    OneSignal.push(["init", {
        appId: "@appId",
        allowLocalhostAsSecureOrigin: true,
        autoRegister: true,
        subdomainName: '@subdomainName',

        httpPermissionRequest: {
            enable: true 
        },
        notifyButton: {
            enable: true,
            size: 'medium',
            position: 'bottom-left',
            offset: {
                bottom: '30px',
                left: '75px',
                right: '0px'
            },
            preNotify: true,
            showCredit: true,
            text: {
                'tip.state.unsubscribed': 'Awe. That hurts my feelings.',
                'tip.state.subscribed': 'You are subscribed. Dont mind me chilling here.',
                'tip.state.blocked': 'That hurts. Truly.',
                'message.prenotify': 'Click me to stay in the loop!',
                'message.action.subscribed': "Thank you for subbing true rakesh. We will keep you up to date.",
                'message.action.resubscribed': "Glad to see you're back.",
                'message.action.unsubscribed': "You won't receive notifications again. Promise. :(",
                'dialog.main.title': 'Manage Site Notifications',
                'dialog.main.button.subscribe': 'NOTIFY ME',
                'dialog.main.button.unsubscribe': 'LEAVE ME ALONE',
                'dialog.blocked.title': 'Unblock Notifications',
                'dialog.blocked.message': "Follow these instructions to allow notifications:"
            }
        },
        welcomeNotification: {
            title: "Welcome to Notifications",
            message: "Thank you for signing up for desktop notifications."
        }
    }])
</script>