Expected Identifier Error

[bkrstirregular]

The sound does play and it's a level door

[Cranky Old Man]

The sound does play and it's a level door

Then you're simply using the wrong function to unlock it.
Try this function instead:
SetLevelDoorLocked(string& asName, bool abLocked);
(Also note that level doors won't swing open.)

[bkrstirregular]

void UsedKeyOnDoor(string &in asItem, string &in asEntity)
{
SetLevelDoorLocked(string& "firstdoor1", true);
PlaySoundAtEntity("", "unlock_door", "firstdoor1", 0, false);
RemoveItem("key_1");
}

So like this?

[Cranky Old Man]

void UsedKeyOnDoor(string &in asItem, string &in asEntity)
{
SetLevelDoorLocked(string& "firstdoor1", true);
PlaySoundAtEntity("", "unlock_door", "firstdoor1", 0, false);
RemoveItem("key_1");
}

So like this?

I don't know that particular function, but definitely more like this:
SetLevelDoorLocked("firstdoor1", false);

[bkrstirregular]

Omg...if you are not the most amazing person ever!! thank you so so much!!