Hi Andriy,
Check below Screen Shot ,are you maintain 'rfcexec' in program name ?
then test your RFC destination , you getting below message .
Check this link ...SAP Library - TREX - Configuration Documentation
Program Name : <disk_drive>:\usr\sap\ECC_<instance_number>\rfcexec.exe
Gateway Host : Host name (with domain name if necessary) or
the IP address of the host on which the gateway is installed.
Gateway Service: Name of the gateway in the form sapgw<instance_number>
Regard's
Smruti