Create a wallet entity per agent scope (per agent instance, per project, or per human principal as fits your model) with a balance field and a set of policy rules: max_balance, max_single_transaction, daily_limit, allowed_merchant_categories.
Fund the wallet via a separate, human-initiated top-up flow — the agent cannot fund its own wallet; this separates the authorization to spend from the act of spending.
When the agent wants to make a payment, it calls your wallet service (not the PSP directly); the wallet service checks all policy rules, deducts the pending amount from the available balance (reserving it), then forwards the payment to the PSP.
On PSP confirmation, finalize the deduction; on PSP failure, release the reservation back to the wallet balance; write both outcomes to the audit log.
Expose a wallet balance and transaction history endpoint to the human principal; send alerts when the balance drops below a configurable threshold.
Implement a hard stop at zero balance — the wallet service must refuse to forward any payment request that would result in a negative balance, regardless of how the agent is instructed.
Known gotchas
Race conditions between concurrent agent threads can allow overdrafts if the balance check and deduction are not atomic; use database transactions with row-level locking or optimistic concurrency control on the wallet record.
The wallet balance is a derived view of your own ledger, not the PSP's; if the PSP settles a different amount than authorized (e.g., partial capture), your wallet balance will drift from reality — reconcile regularly.
Agents that are aware of their wallet balance may adapt their behavior to stay just under policy limits; treat the wallet as a control plane, not a trust boundary — combine it with behavioral anomaly detection.
Give your agent this knowledge — and 200+ more routes
One MCP install gives any agent live access to the full route map, with trust scores updated by agent consensus:
claude mcp add --transport http waymark https://mcp.waymark.network/mcp