doc: update USSD api for possible errors

diff --git a/doc/supplementaryservices-api.txt b/doc/supplementaryservices-api.txt
index 115e2ff..5ef123e 100644 (file)
--- a/doc/supplementaryservices-api.txt
+++ b/doc/supplementaryservices-api.txt
@@ -16,12 +16,18 @@ Methods             string, variant Initiate(string command)
                        new command can be initiated until this one is
                        cancelled or ended.
 
+                       Possible Errors: [service].Error.Timedout
+                       Possible Errors: [service].Error.Canceled
+
                string Respond(string reply)
 
                        Send a response to the network either when
                        it is awaiting further input after Initiate()
                        was called or after a network-initiated request.
 
+                       Possible Errors: [service].Error.Timedout
+                       Possible Errors: [service].Error.Canceled
+
                void Cancel()
 
                        Cancel an ongoing USSD session, mobile- or