Azure Communication Service Fail to Send with URL

Question

Using ACS with a console app based on public sample to send message to multiple recipients, including a URL. This worked for several weeks and then stopped sending without any errors in the console app reported. The sending number is US-based 800 number at $2/month and sending to a known set of recipients. Removing the URL from the message body works. The number shows as "activated" and is apparently verified because this used to work. The URL is an Azure Blob Storage file link. What is the right way to trap for any failure?

This shows as successful:

     Response<IReadOnlyList<SmsSendResult>> smsResponse = await smsClient.SendAsync(
     from: numHere,
     to: numsSend,
     message: $"{messageComplete}" ,
     options: new SmsSendOptions(enableDeliveryReport: true) 
     {
         Tag = "security", // custom tags
     });
 IEnumerable<SmsSendResult> smsResults = smsResponse.Value;
 foreach (var smsResult in smsResults)
 {
     Console.WriteLine($"Sms id: {smsResult.MessageId}");
     Console.WriteLine($"Send Result Successful: {smsResult.Successful}");
 }
 Console.WriteLine(Environment.NewLine);

Thanks.