[Other] Huge Trouble inserting a Mega Evolution with Dynamic Pokemon Expansion

Hello,
I am currently trying to use Leon's Ultimate Rom Base to add a Mega Evolution to Pokemon Fire Red.
I patched the base Rom and am now trying to configure DPE in order to add Mega-Flygon. Here's what happens :
I do necessary edits and compile everything, it works and I get my test.gba and offsets.ini files.

But when I open test.gba in G3T, I encounter several issues :
1-Firstly, no matter the menu I try to open in G3T, I get an error about SoundBasedMoves missing in the .ini files and I am asked if I want to edit the .ini files. I HAVE to click No in order to access the different editors. From what I've read, this issue can be solved after inserting CFRU, so I'm not worrying too much about this.
2-After doing this, when I go to the Items Editor, I can't find the Flygonite item I defined in DPE in the Free Item Slot number 1. I don't know if that's really an issue or if it is normal that I have to make the item in G3T after inserting it in items.h ?
3-The bigger issue is when I go to the Pokemon Editor and go to Flygon, it tells me "an error occured when loading evolution data" . I have verified the edits I made in DPE and can't find what could be causing the issue.

Here's what I edited to add Mega Flygon with DPE :
-included SPECIES_FLYGON_MEGA in species.h with index 0x4F0 and modified NUM_SPECIES accordingly.
-added sprites in graphics and modified sprite_data.h accordingly.
-modified everything required in the "src" section (Coords, Tables, Base Stats, Cry Tables, // commented EXPAND_LEARNSETS, Evolution table, Enemy Elevation Table......)

I can't for the life of me find what I could have done wrong in configuring DPE. I basically followed everything described in the Required Edits file in Leon's Ultimate Base Rom, file by file.
Could anyone help me ?

Thank you for taking the time to read this.

did you add the evolution in evolution table.c? did you add the moveset in learnsets.c?