We are going to make a request as follows:

// SNIPP SNIPP
{
 "config":
 {
 "encoding": "LINEAR16",
 "sampleRateHertz": 44100,
 "languageCode": "en-us"
 },
 "audio":
 {
 "content": "-- BASE64 AUDIO CONTTENT --"
 }
}
// SNIPP SNIPP

Note that the content property under the audio property is the base64 encoded version of the audio. In the same Audio folder, you should find a file named arvind_sample_recording_base64.txt. This is the base64 version of the same audio. You can use an online service such as https://www.browserling.com/tools/image-to-base64 or https://www.base64-image.de/ for converting your own audio to a base64 string.