"exact"— (default) Transfer a fixed amount, locked at signing time. Supports EVM and Solana networks."upto"— Usage-based billing: the client authorizes a maximum amount and the server settles the actual amount charged (≤ max) via Permit2. EVM-only (eip155:*)."batch-settlement"— High-throughput stateful payment channels. Clients deposit once and sign off-chain vouchers per request. EVM-only (eip155:*).