Hello;

You introduce many different notions in your post, lrt's try to clarify them:

First you describe your CPU as a S7-400FH. A S7-400H is a high-availability system, capable of hot-refundancy, and includes fiber-optic comnectors to exchange code and data between the primary and backup CPU of a redundant system. A S7-400F is a failsafe CPU, allowing design of Safety functions up to SIL3, with support from a programming package named S7 F-Systems(6ES7833-1CC46-0YA5).

A S7-400FH system combines redundancy and Safety processing.

The S7-400 family does not support Failsafe IO modules out of their catalog. F-IO modules for a S7-400F system are integrated over Profibus with IM 153-2 (Profibus) or IM 153-4 (Profinet) interface modulrs, and belong to yhe S7-300 family (SM 326). Have a look at the following Application Example, showing how you can set up a SIL3 application with a S7-400FH, with SM326  F-IOs over a network:

https://support.industry.siemens.com/cs/us/en/view/109106504

The following manual will provide information on the SM 326 Safety IO modules for the S7-300 and ET 200M:

https://support.industry.siemens.com/cs/ww/en/view/19026151/51677357579

Hope this helps,

Daniel Chartier