My callflow looks like in RFC doc (please look at screen).

Transferee and Transfer Target stays behing FS.

Should I do something special at FS side to implement such attendet transfer in case Transferor use re-invite/refer method like RFC describes ?

I supposed - not, but weird things happens in the moment FS get REFER.

I expected that FS will just connect Transferee and Transfer Target but... FS start new call (3th) instead of this.. I mean new call to connect Transferee and Transfer Target. But... They are at hold already and I do not need new call...

I just need to connect them.  In theory I can use lua and try to bridge these two sessions between each other but I am not sure it is correct way.

Also I know about att_xfer feature but I can't use that because it require dtmf method.

Please advice