Hey @fbslo, I assumed the burn action need to be carried out in the website, if someone did it onchain using burn method, it won't work. I read through the code, is really simple and straight forward on the smart contract code.
I used to have some code written back in the days when Hive first released, https://github.com/superoo7/BSwap
I created a method call burnToBC, where the params accept username so that the token can be transfer back on blockchain
/**
* @dev Destroys `amount` tokens from the caller.
*
* See {ERC20-_burn}.
*
* Requirements:
*
* - Blockchain `username`
*/
function burnToBC(uint256 amount, string memory username) public {
_burn(_msgSender(), amount);
emit TokenBurnToBC(amount, username);
}