Android Question SIP SendDTMF (sip_callerror)

Hello,

my problem is, that

Private Sub btnDTMF_Click
If CurrentCall.IsInitialized Then
CurrentCall.SendDtmf(10)
End If
End Sub

Click to expand...

does not send DTMF *

The log shows

Logger verbunden mit: samsung SM-G389F
--------- beginning of main
** Activity (main) Create, isFirst = true **
** Activity (main) Resume **
** Activity (main) Pause, UserClosed = true **
sending message to waiting queue (sip_callerror)

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The last line (sending message...) appears after the app is closed.

If I use e.g. Vfone App from Akuvox the DTMF tone is send, so there is no problem with my sip server.

What does sending message to waiting queue (sip_callerror) mean and how can I solve it?

regards
Volker