Adding Modded Joker to Deck

[doctorkelp]

Setup

Suppose I have some custom joker, which is valid.
SMODS.Joker { key = 'j_my_joker' ... }

and I have a custom deck where I'd like to include this custom joker when starting a new run.
SMODS.Back { ... config = { ... jokers = {'j_my_joker'}}

Verified the joker is in a valid state:

My joker works fine if I roll until I find it in the shop.

Problem Statement:

I want my modded joker to be added to my custom deck, in order to tinker with it efficiently. Rolling for it in the shop isn't effective.

Question:

What do I need to do to resolve the center = nil problem in the following error message?

Error snippet

Error:

Oops! The game crashed:
functions/common_events.lua:2295: attempt to index local 'center' (a nil value)

Additional Context:
Balatro Version: 1.0.1n-FULL
Modded Version: 1.0.0~ALPHA-1414a-STEAMODDED
LÖVE Version: 11.5.0
Lovely Version: 0.7.1
Platform: Windows
Steamodded Mods:
    1: Vanilla SMODS by DrKrelp [ID: VSMODS, Version: 1.0.0]
    2: Escape Exit Button by Steamo [ID: EscapeExitButton]
Lovely Mods:
    1: Brainstorm

Stack Traceback
===============
(3) Lua global 'create_card' at file 'functions/common_events.lua:2295'
Local variables:
 _type = string: "Joker"
 area = table: 0x0814aae8  {click_offset:table: 0x0814ac48, children:table: 0x0814b328, shuffle_amt:0 (more...)}
 legendary = nil
 _rarity = nil
 skip_materialize = nil
 soulable = nil
 forced_key = string: "j_my_joker"
 key_append = string: "deck"
 area = table: 0x0814aae8  {click_offset:table: 0x0814ac48, children:table: 0x0814b328, shuffle_amt:0 (more...)}
 center = nil
 ...

Thanks in advance for any discussion / helpful context.

[Eremel]

You need to add your mod prefix to the key, "j_modprefix_my_joker"

[doctorkelp]

Thanks @Eremel for the reply and direct answer. I see that it's referenced here https://github.com/Steamodded/smods/wiki/Mod-Metadata, but it wasn't clear to me that the format should be BalatroPrefixId_ModPrefix_SomeKey given the way it's written. It makes sense now.