For example, when I try a command similar to yours, I get:
++ 3dttest++: AFNI version=AFNI_22.0.21 (Mar 21 2022) [64-bit]
++ Authored by: Zhark++
++ Number of -Clustsim threads set to 8
++ option -setA :: processing as SHORT form (all values are datasets)
++ have 28 volumes corresponding to option '-setA'
++ option -setB :: processing as SHORT form (all values are datasets)
++ have 28 volumes corresponding to option '-setB'
** FATAL ERROR: Cannot use -Clustsim when -prefix has an absolute path
** Program compile date = Mar 21 2022
This clearly tells me what the problem is -- the '-prefix' option starts with a '/' character.
