Paper version git-Paper-248 (MC: 1.16.3) (Implementing API version 1.16.3-R0.1-SNAPSHOT)

ChestShop's version is: 3.11 (build 213)

Economy plugin is MainMC economy

No permission plugins, small server with only friends and everyone is OP

Full Plugin List: ChestShop, FloodGate, Geyser, MainMC, MainMC Economy, Worldedit, Vault

Whats Happening?

but after that it works fine

I cannot re-create this issue with the latest development build and Essentials. Please test the latest build and see if the issue persists, if so then this might be an issue with your economy plugin or maybe you use some special settings. Please provide the rest of the information requested in the issue template (full config and log file) after updating the latest dev build.

EDIT: I took a quick look at MainMC Economy and it looks like they don't properly implement the Vault Economy API so this issue is most likely caused by that. I suggest contacting its author(s) about this issue and request that they make it fully compatible with Vault.