How did you download the content? Can you share some code snippet? Here is some example code using the RingCentral Node JS SDK

async function download_call_recording(){

    console.log("===== download_call_recording ======")

    try{

      const resp = await rcsdk.get("https://media.ringcentral.com/restapi/v1.0/account/1780090xx/recording/89983750xx/content")

      var buf = await resp.buffer();

      fs.writeFile("new_recording.mp3", buf, function(){

        console.log("Done")

      })

    }catch (e){

      console.log(e.message)

    }

}

We try to download using Java client, but even curl is failing, can you check if the resource actually exists? What is the status of the resource?