Transfer problem with cisco spa301

Hi all!
I’ve managed to make a Cisco SPA301 with an asterisk server.
but the call transfer is not working with the phone. It is ok with the softphones (zoiper) an my native android sipphone. i use “**” and “##” for the transfers, i’ve been serching if these keys are used by Cisco for somthing else but i didn’t find anything.
Any help would be appreciated.
thank you.

Please use Asterisk Support for support requests.

Those code are processed by Asterisk, so any phone that can generate those codes should work.