Transfer calls from gateway, no luck


801 calls extension 8000, after asterisk bridged the call.
801 wants to transfer call to 8001. For 3cx phones, no problem.

Does it use the same dialplan? like dial a new number?
which context? same as: 8000 dials 8001?

But using gateway, it did not work.
[Nov 8 14:59:40] WARNING[1911]: chan_sip.c:18325 handle_request_info: Unable to parse INFO message from 7346ed4823cd91c029c46a303dc9a88e@ Content
== Spawn extension (users, 8000, 1) exited non-zero on ‘SIP/801-00000000’

What could be the problem? The gateway has a setting for transfer: internal processing, RFC2833, SIP INFO.
I tries 3 options. Only SIP INFO, asterisk print some error message. Other two options, asterisk keeps silent,
nothing happened.

Thanks for help.