Received the project in private. Oracle is tricky with its types, and mixing with FireDAC, gets trickier.
Thing is you are mapping a string Delphi field to a database field with size 2048. It creates it as VARCHAR but FireDAC mixes it up probably because the types in Delphi are Unicode.
If you try to map the strings to NVARCHAR2 (setting TGlobalConfigs.GetInstance.MapStringToNational char to true, as explained here), Oracle doesn't accept such data type (at least the version I'm using).
I'd suggest you simply map such field to NCLOB, this way:
[Column('N', [], 65536)]
FN: string;
Then it should work fine.