pympp is a Python SDK for the Machine Payments Protocol. Prior to version 0.9.1, when the server acts as the feepayer, pympp validates calldata using ethabi decoding, which is lenient about trailing bytes. The FeePayerPolicy caps gaslimit (≤ 2 M) and maxfeepergas (≤ 100 Gwei) but does not check calldata length. Tempo uses legacy calldata gas pricing: 16 gas per non-zero byte. Appending N bytes of 0x01 padding inflates actual gas used by N × 16 while keeping gaslimit and maxfeepergas within policy caps. The server cosigns and broadcasts the padded transaction, draining its fee-payer wallet. This issue has been patched in version 0.9.1.