Error transcribing audio file

Hi everybody,
We are using speech to text service, and haven't had any problems until yesterday, without having made any changes to our code. Now, when we try to transcribe a mp3 file hosted in our server, we get this error:
{
successfulTranscriptionsCount: 0,
failedTranscriptionsCount: 1,
details: [
{
source: "https://url/mp3/mp3file.mp3",
status: "Failed",
errorMessage: "Connection to the recording URI could not be reestablished",
errorKind: "DownloadRecordingsUrisUnknownError"
}
]
}
There are no changes in our code, there are no problems with permissions because is possible to access all mp3 files from a browser, and we don't understand what that error means. Any help will be welcome.
Thanks!!
Thank you for your reply!
We have tried with multiple mp3 files, some of them were working fine last week, so it doesn't seem to be a problem with resources.
Regards
Another clue: uploading files to another server, we can transcribe with no problems. The url in our server is public, the file is public too and can be downloaded directly from the link of the error, and no changes has been made to server, firewall, etc. If you need the real url of a file let me know how send it to you.
Thanks!