You can solve this by 2 ways.
1. Deleting "signininfo.json" file from "..\WebAppBuilderForArcGIS\server" folder.
2. Updating this file and providing right "appId" for you application.
You can get the appID from your portal. Safest way is to get client id and provide it in url.
Ex of : "signininfo.json"
[
{
"portalUrl": "https://XXX.domin.com/portal",
"supportsOAuth": true,
"isWebTier": true
},
{
"portalUrl": "https://XXX.domin.com/portal", // Update it with your portal url
"supportsOAuth": true,
"isWebTier": false,
"appId": "ABZlRO2HW2nJ0qYH" // Provide your registered appid.
}
]