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

travelersbackpack-forge-1.20.1-9.1.30.jar

1. Describe the bug
   1.20.1 Forge Server Can't use if "backSlotIntegration" is "false"（I'm pretty sure it's false in my server）
   Put backpack on the ground and Shift + Rightclick can show in GUI but can't open backpack（It tell me "equip it in the back slot"）
   Put it in "back" slot also can't open（Single Player game can open it）

2. Write steps to reproduce the bug
   Open serverconfig/travelersbackpack-server.toml edit it
   backSlotIntegration = false
   All the backpack can't use if not on player's hand

3. What is expected behaviour
   I don't know...maybe?

4. Screenshots (If applicable)

Hey, if you play on server, you have to change this config option on server not in your mc config.

Oh, sorry I've misread

1. Make sure you change config setting when server is off, change settings, hit save and then start
2. If it still doesnt work, try checking your config folder in server files, see if there's file travelersbackpack-common (or anything config related to travelersbackpack) - if so, delete these files. Try again after removing the files

I'm certain the setting works, so there must be some problem in installation I think.
Also make sure you use mod "Curios" and not "Accessories"
Accessories is compatible for 1.20.1 only if using curios compat layer. Theres no standalone integration from tb for accessories 1.20.1

1.Yes, the server was closed when I edited it
2.Server files "config" folder have "travelersbackpack-common.toml". But it just has 2 options "enableLoot" and "enableVillagerTrade"

###travelersbackpack-common.toml###
#Common config settings
[common]
#Enables backpacks spawning in loot chests
enableLoot = true
#Enables trade for Villager Backpack in Librarian villager trades
enableVillagerTrade = true

When backSlotIntegration is true : backpack can use in "back" slot （curios-forge-5.12.0+1.20.1.jar）and can in the main hand and rightclick
When backSlotIntegration is false : backpack just can open in the main hand and rightclick

Now on the server, I've set it to true and added a "back slot" as a temporary solution.
I hope this solution can help other players who are experiencing the same problem.

Oh, I think I know what you mean:

If backSlotIntegration is set to false, you have to equip backpack with button inside backpack gui
Please see here:
https://github.com/Tiviacz1337/Travelers-Backpack/wiki#equip-backpack