BigchainDB issue with send_commit

Question

I am learning BigchainDB and I am trying to store a payload on the blockchain with the following code:

alice = generate_keypair()
metadata = {'planet': 'earth'}
bicycle = {
   'data': {
    'bicycle': {
         'serial_number': 'abcd1234',
         'manufacturer': 'bkfab',
    },
    },
}
tx = bdb.transactions.prepare(
    operation='CREATE',
    signers=alice.public_key,
    asset=bicycle,
    metadata=metadata,
)
signed_tx = bdb.transactions.fulfill(tx,private_keys=alice.private_key)
sent_creation_tx = bdb.transactions.send_commit(signed_tx)
return sent_creation_tx

I got a 500 from the send_commit.

What I am doing wrong?