ddlnotfound exception - what is the problem?

I faced weird issue - I have 2 lib that I put under Assets\Plugins\Android, first lib name is mylibrary and second one - libtetdecoder.

Then I try to use them with the same way and I see that I can invoke methods from first one and can't from second one, because of this error

     (Filename: <d25e5b88a8b44b89b27c70e01a22f338> Line: 0)
 2020-09-15 09:39:53.243 26169-26207/? E/Unity: DllNotFoundException: libtetdecoder
         at (wrapper managed-to-native) TestScript.foolib()
       at TestScript.Update () [0x00021] in <d25e5b88a8b44b89b27c70e01a22f338>:0 

There is how I use these libs:

 using UnityEngine;
 using System.Runtime.InteropServices;
 using UnityEngine.UI;
 using System.Globalization;
 
 public class TestScript : MonoBehaviour
 {
     public Text myText;
     public Text myText2;
     private const string pluginNameFirst = "mylibrary";
     private const string pluginNameSecond = "libtetdecoder";
 
     //native interface
     [DllImport(pluginNameFirst)]
     private static extern int foo();
 
     //native interface
     [DllImport(pluginNameSecond)]
     private static extern int foolib();
 
     // Start is called before the first frame update
     void Start()
     {
         
     }
 
     // Update is called once per frame
     void Update()
     {
         int i = foo();
         myText.text = "HERE : " + i;
 
         int il = foolib();
         myText2.text = "HERE : " + il;
     }
 }

 

What is a possible issue?