I searched the forum about this but all posts are well over a year old, and none have a solution.
On my website, all users that register are being marked as alt, and I cant find any way to set main characters/accounts. If someone can help me out, it would be greatly appreciated

I'm stabbing in the dark because I don't have this issue but I'll try a couple of obvious things.

1) Under your admin panel Characters and Accounts check the Character - Account Association. You want to make sure that all the characters are associated to the right account.

2) Under your admin panel Character and Accounts go to the Characters option. If you edit each one you need to make a main it should have a drop down menu option for changing the character from alt to main.

This is all I see

So when you setup your game (Admin -> Games -> Games) there is a question that says "Could someone have alternate characters (alts) in this game?" with answers of yes and no. If you click edit on the game that people are registering on your site for ensure this option says yes. I would think it would default to main if you can't have alts however if this got changed somewhere along the way I could see where it might cause an issue if. If it is not set to yes try setting it to yes and see if that shows the edit field on your character edit page.

setting it to yes allowed the field. Though I dont think that the game will allow alts, I think I'll just leave that set to 'yes'
thanks

Glad that worked.

Chops,
This looks like maybe a small bug somewhere.

Indeed. The idea of an alt shouldn't matter when the field isn't needed, so it should pretty much always be hidden.