Unable to find extension when forwarding from spa3000 ATA

Here’s my extensions.conf

exten => _7.,1,Dial(SIP/skypetestuser/${EXTEN:1})

exten => steven,1,Ringing
exten => steven,2,Dial(SIP/steven,,120)
exten => steven,4,Hangup

exten => 501,1,Dial(SIP/steven)
exten => 502,1,Dial(SIP/spa3000)
exten => 503,1,Dial(SIP/mum)

exten => spa3000,1,Ringing
exten => spa3000,2,Dial(SIP/spa3000,20,T)
exten => spa3000,4,Hangup

include => dialout
exten => _0[1278]XXXXXXXXX,1,Dial(SIP/${EXTEN}@spa3000,60,)
exten => _0[1278]XXXXXXXXX,2,Congestion
exten => _[2-8]XXXXXX,1,Dial(SIP/${EXTEN}@spa3000,60,)
exten => _[2-8]XXXXXX,2,Congestion

exten => _07XXXXXXXXX,1,Dial(SIP/${EXTEN}@pstn-spa3k,60,)
exten => _07XXXXXXXXX,2,Congestion

exten => _1471,1,Dial(SIP/${EXTEN}@spa3000,60,)
exten => _1471,2,Congestion
exten => steven,2,Dial(SIP/steven,300,T)
exten => steven,4,Hangup

exten => mum,2,Dial(SIP/mum,300,T)
exten => mum,4,Hangup

On the pstn tab of sipura/linksys spa3000 I gave it the following sip url as a dial plan
Asterisk acknowledges the phone is ringing however in the logs I get an error saying it can’t find the extension steven. However if I dial that extension from a different extension it rings. Why?

What’s the actual error message. I don’t see why this should even attempt to call a non-numeric extension.