Error posting to web api on Azure using zumo on unity

We have an error using some plugin on unity. it worked for a few years, suddenly at 1.6.18 stopped working.

we are using webapi through azure app service. the error is :

{System.Net.WebException: Error getting response stream (Write: BeginWrite failure): SendFailure ---> System.IO.IOException: BeginWrite failure
at System.Net.Sockets.NetworkStream.BeginWrite (System.Byte[] buffer, Int32 offset, Int32 size, System.AsyncCallback callback, System.Object state) [0x00000] in <filename unknown>:0
at Mono.Security.Protocol.Tls.RecordProtocol.BeginSendRecord (ContentType contentType, System.Byte[] recordData, System.AsyncCallback callback, System.Object state) [0x00000] in <filename unknown>:0
at Mono.Security.Protocol.Tls.RecordProtocol.SendRecord (ContentType contentType, System.Byte[] recordData) [0x00000] in <filename unknown>:0
at Mono.Security.Protocol.Tls.RecordProtocol.SendAlert (Mono.Security.Protocol.Tls.Alert alert) [0x00000] in <filename unknown>:0
at Mono.Security.Protocol.Tls.RecordProtocol.SendAlert (AlertDescription description) [0x00000] in <filename unknown>:0
at Mono.Security.Protocol.Tls.SslStreamBase.AsyncHandshakeCallback (IAsyncResult asyncResult) [0x00000] in <filename unknown>:0
--- End of inner exception stack trace ---"

 

Is 1.6.18 a date value?

 

Hi,
It means that on June 1st, 2018, it all stopped working for us.