Error with standard adaptive card

[cbourdon]

Hi all - I'm trying to set up a VERY simple adaptive card to remind team members of a specific task and have one person "claim" the task by clicking the button. I'm planning to update the card in a future step with the name of the person who clicked, but for now I can't even get the card to work. I've taken out all the variables and reduced it to just bog-standard content but still no luck. Here's how the designer view of it looks along with the rest of the flow. The flow condition is just checking the email for a specific string: 

 

And here's the JSON for the card. Note that I haven't edited the JSON at all, and I don't even have permissions to do so. 

{

  "type": "OpenApiConnectionWebhook",

  "inputs": {

    "parameters": {

      "poster": "Flow bot",

      "location": "Group chat",

      "body/body/messageBody": "TESTING",

      "body/body/updateMessage": "Thanks for your response! ",

      "body/body/recipient/recipient": "19:339229b70b4646c8b82078d42592cc06@thread.v2"

    },

    "host": {

      "apiId": "/providers/Microsoft.PowerApps/apis/shared_teams",

      "connection": "shared_teams",

      "operationId": "PostCardAndWaitForResponse"

    }

  }

}

Finally, here is the full error I receive when it runs: 

The request failed. Error code: 'InvalidJsonInBotAdaptiveCard'. Error Message: 'Microsoft.Azure.ProcessSimple.Data.Entities.Exceptions.ProcessSimpleDataException: The specified Teams flowbot adaptive card request is missing or invalid. The tracking Id is '{0}'. ---> Newtonsoft.Json.JsonReaderException: Unexpected character encountered while parsing value: T. Path '', line 0, position 0.
at Newtonsoft.Json.JsonTextReader.ParseValue()
at Newtonsoft.Json.Linq.JObject.Load(JsonReader reader, JsonLoadSettings settings)
at Newtonsoft.Json.Linq.JObject.Parse(String json, JsonLoadSettings settings)
at Microsoft.Azure.ProcessSimple.Data.Components.AdaptiveCards.AdaptiveCardBuilder.DeserializeAdaptiveCard(String serializedAdaptiveCard, RequestIdentity requestor, CultureInfo cultureInfo, BotAdaptiveCardAtMentions atMentions) in C:\__w\1\s\src\processsimple\Roles\ProcessSimple.Data\Components\AdaptiveCards\AdaptiveCardBuilder.cs:line 647
--- End of inner exception stack trace ---
at Microsoft.Azure.ProcessSimple.Data.Components.AdaptiveCards.AdaptiveCardBuilder.DeserializeAdaptiveCard(String serializedAdaptiveCard, RequestIdentity requestor, CultureInfo cultureInfo, BotAdaptiveCardAtMentions atMentions) in C:\__w\1\s\src\processsimple\Roles\ProcessSimple.Data\Components\AdaptiveCards\AdaptiveCardBuilder.cs:line 670
at Microsoft.Azure.ProcessSimple.Web.Common.Validation.BotAdaptiveCard(String card, RequestIdentity senderRequestIdentity) in C:\__w\1\s\src\processsimple\Roles\ProcessSimple.Data\Common\Validation\BotValidation.cs:line 882'.

I've been scratching my head on this for a while, so any help is greatly appreciated! Happy to send more screenshots if needed.