I've been trying to create a simple wallet smart contract by myself to learn FunC, but my transactions keep failing with exit code 34. What am I doing wrong?

() recv_external (slice in_msg) impure {
    var valid_until = in_msg~load_uint(32);

    throw_if(35, valid_until <= now());

    var dest_addr = in_msg~load_bits(256);

    var msg = begin_cell()
        .store_uint(0x18, 6)
        .store_slice(dest_addr)
        .store_coins(1)
        .store_uint(0, 1 + 4 + 4 + 64 + 32 + 1 + 1)
    .end_cell();

    accept_message();

    send_raw_message(msg, 3);
}

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