Help in GameMaker

For my Opera GX Game Jam game, I'm receiving this error. Please help :(

Variable <unknown_object>.jumping(100003, -2147483648) not set before reading it.

at gml_GlobalScript_scr_jump_check (line 1) - if (jumping)

gml_GlobalScript_scr_jump_check (line 1)

Heyy guys we are new programing (like very noobs) and we are looking for someone (not necessarily profesional) who can help us!! We are two people and we speak english and spanish (spanish is our first language) if u are interesated feel free to dm me!

pode enviar vários jogos?

I am joining the Opera GX Game Jam contest and I don't know much about GML but I might be able to make something, I'm looking to see if anyone is good at pixel art/GML coding and wants to help. You can reply here or message me on Discord @Spidey #2021

Are there any resolution(room size) limitations for the opera game jam submissions? or some kind of screen ratios?

Can someone well I guess?

Are games for the competition supposed to have a title/options screen, i assume not since they are for the offline screen.

How can i send the game when its done?

About the Opera GX game jam:

Me and some friends want to join the contest, should each of us register or only one must register?

I want to try and make a game for the Opera GX Gamejam, im not 100% with GMS yet but I am learning it and am confident in coding, the only problem is, im not great at Pixel art. If your good with pixel art, msg here or dm me on Disc: Super ShadistarY#8472