Digitmap Question Inbound call route

[larrybob]

To forward a call from my cell to a number in one stage, the following works as expected:
{(14159944803):sp2(558585251164)}

Then User defined Digit maps:
callto :(558585251164)
callthru (14159944803)

THIS WORKS: {(Mcallthru):sp2(558585251164)}

THIS DOES NOT WORK!: {(Mcallthru):sp2(Mcallto)}

What did i do wrong!  Thanks Larry

[RonR]

The (optional) target used in a terminal object of an InboundCallRoute rule may only be a number-to-call OR $2.  It cannot be a DigitMap.

sp2(Mcallto) will literally send 'Mcallto' to the SP2 service provider, not the contents of a User Defined DigitMap named callto.