Attended transfer as default on refer

I’m using MicroSIP and SFLphone as SIP softphones. Both has ability to transfer calls with special button.
When I enter exten and press it, softphone sends REFER udp package and then hungs up - so, it is blind transfer.
I want to use attended transfer instead. Is it possible?

Asterisk supports REFER/Replaces. I’ve no idea about your soft phone. Any SIP hard phone would.