I have also tried the method on the link and it didn’t work for me.
By the way, I thought rbs_sci mentioned this thread after your reply so I revisited here too late.
In the thread, Flow tried the same way I did first(just submitting .gain file).
In my case, it gave me properly gain-corrected images but the images were with defect lines.
After the motion correction, the lines disappeared and the further processing steps are working well by now.
Anyway, thank you for your help, and happy new year!