Look up the CometBFT block limits active at a historical height
A chain can change consensus parameters after launch. The genesis file alone may give a wrong limit for an incident several upgrades later.
Ask for the parameters at the incident height
Set RPC to the chain’s HTTP RPC and choose an available block height. Read block.max_bytes and block.max_gas in the returned consensus_params. Preserve the response height with the values.
curl -fsS "$RPC/consensus_params?height=12000"
If max_gas is -1, the consensus block parameter does not impose an aggregate gas limit. A numeric value such as 40,000,000 sets a block gas budget. These values have different units from max_bytes.
Diagnose transaction admission independently
A transaction can still fail because of application checks, local mempool settings or fee requirements. For a large transaction, also allow for block overhead. The maximum block byte count is not a promised size for an individual transaction. github.com CometBFT RPC