In this guide, you will find out how to open The Blue Barrier in Shelter by Linda in Tower of Fantasy.
There’s one over here on the back of the lorry and it says the last digit is 7.
Then from the back of the truck, you need to go back up to where the NPCs are. You will find the next chest on top of the shelter at the back.
Jump up there again and read it. So the second digit is 6.
Then the next one is on top of the crane at its back, as shown in the image below. It says the second to the last digit is 4.
Now the fourth one could not be found, so you just have to use the process elimination method. In order to open the door, you should not be in the middle of the mission.