0. ALWAYS PROVIDE INFORMATION ABOUT MODLOADER (Fabric / Forge) AND MOD VERSION (For Example 1.19.2-8.2.10)

Modloader : Fabric , Mod version : travelers-backpack-1.20-9.0.2

1. Describe the bug

At the smithing table, I'm not able to upgrade from the leather tier to iron and iron to gold etc..

2. Write steps to reproduce the bug

Using the smithing table for upgrade any tier

3. What is expected behaviour

Backpack be able to be upgraded

4. Screenshots (If applicable)
   

open backpack first in hand, then upgrade, also leather is required in first slot

Not sure to understand what you're meaning. can you add some explanation on the page of the mod or here? please