If you want to use the manual flaps model, you need these things:

1) Download fastman92 limit adjuster (required for manual flap models)
link:
https://www.mixmods.com.br/2022/01/fastman92-limit-adjuster/

2) Install fastman92 limit adjuster, just copy all the contents of the "$fastman92 limit adjuster" folder to your GTA SA folder.

3) Back to 'SA_B738NG_WL_ADV26' folder, open 'Required for this mod', now open 'fastman limit adjuster settings' folder and copy its contents to your
   GTA SA folder

4) If you have your personal settings in fastman92 limit adjuster, so, you need to change these things:

A. Go to your GTA SA folder, open 'fastman92limitAdjuster_GTASA.ini' and look for this parameter:

[ID LIMITS]
; Apply ID limit patch (0)
#Apply ID limit patch = 0

Now change this first parameter to this:

[ID LIMITS]
; Apply ID limit patch (0)
Apply ID limit patch = 1

B. Now do the same with this parameter:

; Enable model special feature loader (0)
#Enable model special feature loader = 0

Now change this second parameter to this:

; Enable model special feature loader (0)
Enable model special feature loader = 1

C. The last step now, go to your GTA SA folder, open 'data' folder and open 'model_special_features.dat', now add this value at the end of the text:

at400 androm

Now save your settings and the cargo doors or manual flaps will work :D 