This article explains that IPSec VPN transport mode is currently not supported on SRX devices.
SRX supports IPSec VPN in tunnel mode. In the configuration, there is no option for transport mode. Does the SRX support a VPN in transport mode?
As of now IPSec VPN in transport mode is not supported on SRX devices. Please contact the sales/accounts team to get the roadmap on this feature.
For a list of supported features, go to the SRX Technical Documentation and select the Feature Support Reference.