The specified value is unknown. [Error Code: TypeCasting.UnknownCasting] when calling API to get file

I think i got a bit further now.

I am now returning a base64 string from my api an not a filecontentresult.

I am creating the string like this: "data:text/calendar;base64," + Convert.ToBase64String(myBytes)

Now the workflows successfully calls the xtension, but when i try to send the received attachment via mail, i get the error “[WorkflowExecution.Runtime.Internal] The workflow failed unexpectedly.”

The received object is structured like this:

When i send the objICSFile the mail successfully sends, but without any attachments, and when i send the Content the mail runs into the error above.

Hi ​@NiklasG,

I was recently playing with the Nintex API and exporting workflows.
I found that configuring my response as per the below put the file into a file variable, which I could then use downstream in the workflow.
Maybe this might work for you.
 

                "responses": {
                    "200": {
                        "description": "Successful download",
                        "schema": {
                            "type": "file"
                        }
                    },

Hi ​@NiklasG have you solved this error?