Where can I find the encryption algorithm for this POST request in an Android APP?

Question

I have an Android app for which I need to mock an API call outside of that environment. I successfully killed the certificate pinning on this app with Frida in order to access the URL and more, but now I face another obstacle.

The information on the POST request is encrypted or hashed with something in the client, I just don’t know what is it.

This is the view (it's in Spanish so I leaved the text as it is in order to search through its labels):

This is how the POST request looks when its sent from the app when I enter an amount to send (think of it as app currency) to another peer registered in this same app. So I suppose it's encrypting the contact data and the amount:

{
  “content”: “a1b80843068b4ba6e99eb13e165e907695884416c2365a713d3805c1a1b62f45ad13b623b04a93aac19daf5d9280f6b0d0ab96fcce312fefc7f1e53ec3705917b2f5dbb867030006de295053bfc1c8efad9d255aa05a21be4f3da1b4eb3d0448d215e4f47cad89a1d91a3e255fcb5d9f6d3418d33c91e7d3e91404b9a4d8596fe80bffb31509a22958070893eef18a088764155d3a”,
    
      “tag”: “1beede6ca014d893e234a1ff6d1dc317”,
    
      “iv”: “e5391ed0df5cd71b3472d93b”
}

I managed to found the smali code where this is done by searching the JSON labels, I used jadx-gui for this, here is the apk used (is an app bundle so I only included the base.apk), it can be opened with jadx-gui:

https://www.mediafire.com/file/myzjnoim974x107/base.apk/file

Here it is the decompiler jadx version of it:

https://www.mediafire.com/file/3gupjge3l2h0hpb/decompiled-with-jadx.zip/file

And this is the Google Play Store link:

https://play.google.com/store/apps/datasafety?id=cl.bci.sismo.mach&hl=en&gl=UK

As I’m reading through this code (at sources\p427p7\MessageEncryptedModel.java) I can see that is converting the strings into this encrypted format, but I don’t understand how when looking at the package imported, which is being used for this:

package p427p7;

import com.google.gson.annotations.Expose;
import com.google.gson.annotations.SerializedName;
import ia0.C8465k;

/* renamed from: p7.a */
/* loaded from: classes.dex */
public final class MessageEncryptedModel {
    @SerializedName("content")
    @Expose

    /* renamed from: a */
    private String f36230a;
    @SerializedName("tag")
    @Expose

    /* renamed from: b */
    private String f36231b;
    @SerializedName("iv")
    @Expose

    /* renamed from: c */
    private String f36232c;

    public MessageEncryptedModel(String str, String str2, String str3) {
        C8465k.m23334f(str, "content");
        C8465k.m23334f(str2, "tag");
        C8465k.m23334f(str3, "iv");
        this.f36230a = str;
        this.f36231b = str2;
        this.f36232c = str3;
    }

    /* renamed from: a */
    public final String m11426a() {
        return this.f36230a;
    }

    /* renamed from: b */
    public final String m11425b() {
        return this.f36232c;
    }

    /* renamed from: c */
    public final String m11424c() {
        return this.f36231b;
    }
}

Does anyone have an idea of how this JSON data is being encrypted before being sent? I have tried to understand through the package code by replicating it but I can't find a hardcoded key