Body always empty when answering an invoke - microsoft-teams

Question

I have a live Microsoft Teams application with a couple of working functionalities. Right now I am working on a new feature where the user clicks on a button in a previously sent adaptive card and I will open another adaptive card with a form for the user to fill. I am using this documentation as a base, which has a really similar example as to what I am trying to achieve here.
Since I am working with an adaptive card the button that will open my form card is an Action.Submit button with "msteams": {"type': 'task/fetch"} inside its data. When I click that button I receive the correct invoke call, the body looks like this:
{
"type": "invoke",
"timestamp": "2021-02-01T20:19:34.327Z",
"localTimestamp": "2021-02-01T15:19:34.327-05:00",
"id": "f:955407977095344101",
"channelId": "msteams",
"serviceUrl": "https://smba.trafficmanager.net/amer/",
"from": {
"id": "censured",
"name": "censured",
"aadObjectId": "censured"
},
"conversation": {
"conversationType": "personal",
"tenantId": "censured",
"id": "censured"
},
"recipient": {
"id": "censured",
"name": "Tcensured"
},
"entities": [
{
"locale": "censured",
"country": "censured",
"platform": "censured",
"timezone": "censured",
"type": "clientInfo"
}
],
"channelData": {
"tenant": {
"id": "censured"
},
"source": {
"name": "message"
},
"legacy": {
"replyToId": "censured"
}
},
"replyToId": "censured",
"value": {
"commandId": "reply_feedback",
"requested_feedback_id": 1,
"type": "composeExtension/fetchTask"
},
"locale": "censured",
"localTimezone": "censured"
}
It seems like the invoke call is correct, so the next step is to answer the call with my adaptive card. However, it doesn't matter what I answer this call with, when I inspect the invoke call in my browser the answer is always empty, even if I answer with a really simple task response like (which I got from the documentation)
{
"task": {
"type": "continue",
"value": {
"title": "Task module title",
"height": 500,
"width": "medium",
"url": "https://contoso.com/msteams/taskmodules/newcustomer",
"fallbackUrl": "https://contoso.com/msteams/taskmodules/newcustomer"
}
}
}
Or even
{
"task": {
"type": "message",
"value": "Test"
}
}
I still get an empty response on the front-end side. I am fairly confident that I am properly answering the call on my side with data, I have a lot of other features in this same application working so I don't think it is some problem where I am actually giving an empty body from my side. Maybe for the specific invoke call I need to answer things in a different manner?
Obs: I am using Python with no SDKs, so I build Adaptive Cards and interpret the requests on my application.