Change request body using script

[Peter84]

Hello. I am changing the post request body through a script:

static function OnBeforeRequest(oSession: Session) {

        if (oSession.fullUrl=="https://www.example.com/api/v1/device") {
            var rep = System.IO.File.ReadAllBytes("replace.txt");
            oSession.requestBodyBytes = rep;
        }

 

If I do not change the request body, the server accepts it (301). If I use a script, the server throws an error (401). The data in replace.txt is completely identical to the data from the original request that the server accepts. What could be the problem?

[Peter84]

The issue is resolved. It's not about Fiddler. MITMEngine is running on the server, which is why there is an error when replacing data.