    function register(address _recipient) public onlyUnregistered returns (uint256 tokenId) {
        address smartContract = msg.sender;

        if (_recipient == address(0)) revert InvalidRecipient();

        tokenId = _tokenIdTracker.current();
        _mint(_recipient, tokenId);
        _tokenIdTracker.increment();

        emit Register(smartContract, _recipient, tokenId);

        feeRecipient[smartContract] = NftData({
            tokenId: tokenId,
            registered: true
        });
    }
    function assign(uint256 _tokenId) public onlyUnregistered returns (uint256) {
        address smartContract = msg.sender;

        if (!_exists(_tokenId)) revert InvalidTokenId();

        emit Assign(smartContract, _tokenId);

        feeRecipient[smartContract] = NftData({
            tokenId: _tokenId,
            registered: true
        });

        return _tokenId;
    }
