Submitted by: @pavel-zotov

Specifying of character sets as mandatory for these command switches, e.g:

gbak.exe -c -FIX_FSS_METADATA win1252 -FIX_FSS_DATA WIN1252 some.fbk new_target.fdb

WIthout these arguments gbak display messages that not related to MISSING of that argument ('not found' <> 'required'!).

Furthermore, messages differ depending on what it was specified first: -FIX_FSS_DATA or -FIX_FSS_META:

1) gbak.exe -c -FIX_FSS_DATA -FIX_FSS_METADATA some.fbk localhost/3050:c:\temp\new_target.fdb ==>
gbak: ERROR:Character set -FIX_FSS_METADATA not found
gbak:Exiting before completion due to errors

2) gbak.exe -c -FIX_FSS_METADATA -FIX_FSS_DATA some.fbk localhost/3050:c:\temp\new_target.fdb ==>

gbak: ERROR:bad parameters on attach or create database
gbak: ERROR: CHARACTER SET -FIX_FSS_DATA is not defined
gbak: ERROR:failed to create database localhost/3050:c:\temp\new_target.fdb
gbak:Exiting before completion due to errors

It will be good to add samples in official doc when proper usage is shown.
For instance, in Windows command may looks like this ( '^' is used for split parts of long command; it is valid in Windows batches and similar to usage of '\' on Linux shell scripts):

gbak.exe ^
-c ^
-fix_fss_metadata win1252 ^
-fix_fss_data win1252 ^
c:\mix\firebird\qa\fbt-repo\tmp\test.fbk ^
localhost/3254:c:\mix\firebird\qa\fbt-repo\tmp\test.fdb