unsupported_file
What happened
Conversion accepts MQL5 source files, with the extensions .mq5 and .mqh, sent as the raw body of the request. Anything else, or a request with no file body, is refused with 400. The reply can carry a reason.
What to do
Send the indicator's own .mq5 source file, or an .mqh file it includes.
Example
json
{
"error": "A raw file body is required.",
"code": "unsupported_file"
}