Teams App with Bot (WebChat) is not installable

We should install a Microsoft Teams App for our customer. It is a chat bot with webchat, the web chat is working in browser but installation as Microsoft Teams App failed.

we used this manifest-file for installation anonamized with a few text parts.

{
  "$schema": "https://developer.microsoft.com/en-us/json-schemas/teams/v1.9/MicrosoftTeams.schema.json",
  "manifestVersion": "1.9",
  "version": "1.0.0",
  "id": "******-****-****-****-***********",
  "packageName": "tdo.chatbot1",
  "developer": {
    "name": "XXX YY",
    "websiteUrl": "https://xxxx.yyy",
    "privacyUrl": "https://xxxx.yyy",
    "termsOfUseUrl": "https://xxx.yyy",
    "mpnId": "111111"
  },
  "icons": {
    "color": "color.png",
    "outline": "outline.png"
  },
  "name": {
    "short": "chatbot1",
    "full": "chatbot1"
  },
  "description": {
    "short": "A Teams App with Bot",
    "full": "TestBotTeams"
  },
  "accentColor": "#40497E",
  "staticTabs": [
    {
      "entityId": "conversations",
      "scopes": [
        "personal"
      ]
    },
    {
      "entityId": "about",
      "scopes": [
        "personal"
      ]
    }
  ],
  "bots": [
    {

      "botId": "*******-****-****-****-************",
      "scopes": [
        "personal"
      ],
      "supportsFiles": false,
      "isNotificationOnly": false
    }
  ],
    "permissions": [
        "identity",
        "messageTeamMembers"
    ],
  "validDomains": []
}

The App Registration for the botid is build with default setting (only a secret was created and it was switched beteween single tenant and multi-tenant for testing).

This installation dialog shows the info of the App shown before adding it to MS Teams.

After clicking "Add" this error will occur.

We deployed the same bot in our tenant and installed the teams app without problems in our Microsoft Teams.

On the customer side a customer employee with enough right try to install this App but failed, then we got the permission to do do it with a test user in their teams, but we failed too. Same message.

The error message has no details, so I am complete without ideas how to fix it.

I think it is permission problem.

But if so how can we get more information and determine which permissions are missing.

Update: It is not at the project end phase where we must deliver a well-formed app. It is only to show that the basic chatbot (LUIS & qna) will work in teams, no other functionallity is required at the moment, so the minmal manifest is needed not the well-formed. If there are parts which avoid installation so it is importand but parts for are not.

I hope someone can help me.

The old depreacreated Web App Bot resource, only buildabel with old arm script will avoid installing as teams app. Using the new azure bot and it will work.