Compose extension is throwing error : V3 agent not found - botframework

Question

I am new to creating Compose Extensions in Teams and am facing an issue when I add it to my Teams.
All the configurations are in place, from registering the Bot to hosting it as a Bot Service on Azure and handling the compose extension query in the code. I have shared the Bot Id in the manifest and given the bot hosted URL with /api/messages appended to the endpoint URL.
The bot as a standalone application works locally as well as on the Azure Porta. I have successfully remote debugged it as well. However, as soon as I sideload it in Teams as a messaging extension, the query is not firing appropriately.
While typing, it stops and shows "Something went wrong with this app. Try Again".
Moreover, when we load the Compose Extension it should make an initial hit to the hosted bot application, I have the debuggers in place and it neither hits the Constructor nor the Post method.
I am getting a 404 error saying V3 agent not found and a failed POST request.
Anyone who might have faced a similar issue and has recovered from it, or may know where I may be going wrong kindly provide your advice. Highly appreciated.
{
"$schema": "https://statics.teams.microsoft.com/sdk/v1.2/manifest/MicrosoftTeams.schema.json",
"manifestVersion": "1.2",
"version": "1.0.0",
"id": "f3c14e30-0af2-4f96-b714-5d258edcab47",
"packageName": "net.azurewebsites.fetchassistant",
"developer": {
"name": "abc",
"websiteUrl": "https://fetchassistant.azurewebsites.net",
"privacyUrl": "https://fetchassistant.azurewebsites.net",
"termsOfUseUrl": "https://fetchassistant.azurewebsites.net"
},
"icons": {
"color": "color.png",
"outline": "outline.png"
},
"name": {
"short": "FetchAssistant",
"full": "Fetch Assistant"
},
"description": {
"short": "abc",
"full": "xyz"
},
"accentColor": "#235EA5",
"composeExtensions": [
{
"botId": "Microsoft App/Bot Id",
"scopes": ["personal", "team"],
"commands": [
{
"id": "FirstName",
"description": "Search Relevant Documents",
"title": "Get Name Division",
"initialRun": false,
"parameters": [
{
"name": "xyz",
"description": "Get Name Division",
"title": "Names"
}
]
}
]
}
],
"permissions": ["identity", "messageTeamMembers"],
"validDomains": ["*.microsoft.com", "*.azurewebsites.net"]
}

Answer 1

I was able to get through the issue you're facing by doing the following:
Navigate to https://dev.botframework.com/bots/
Click on the Microsoft Teams icon in the "Add a featured channel" section
Register your app

Answer 2

I was getting this error myself on an extension.
Following the idea of adding channels, I went to the channels section.
There was no Teams channel configured.
So, I added it.
And the error went away as my extension loaded.