Trunk can not find incoming extension in asterisk-GUI

I tried to create a simple PBX setup with one external SIP trunk(getonsip) to my existing Asterisk PBX box. I did a clean install and configured everything Asterisk-related only by means of Asterisk GUI. Local calls between extensions work fine as well as outgoing calls to my PBX. But when incoming call arrives it always ends up with the following error:
" calls to extension ‘s’ rejected because extension was not found in context"

DID number:

host =
username = nuevo
secret = ***********
trunkname = getonsip ; GUI metadata ; GUI metadata
context = DID_trunk_1
hasexten = no
hasiax = no
hassip = yes
registeriax = no
registersip = yes
trunkstyle = voip
outboundproxy =
fromdomain =
fromuser = nuevovoip
authuser = getonsip_nuevovoip
insecure = port,invite
disallow = all
allow = ulaw,alaw,gsm,g726


include = DID_trunk_1_default

exten = _X.,1,Goto(default,6000,1)

when to use “_X.” and “s” pattern matching in incoming calls

Please contact your supplier (Synology?) as Asterisk GUI has not been supported for several years now, so anyone supplying it should be expected to support it themselves.

s is used to match calls where there is no destination number, e.g. for SIP when the SIP URI has no user part, or for incoming analogue lines which have no means of signalling a destination number.