docs: document paymentRail option for transfer-out

[claude]

Summary

• Updated send-payment.mdx to show the new optional paymentRail field in transfer-out examples
• Updated same-currency.mdx snippet with matching changes
• Added tip explaining that paymentRail is optional and describing when to use it

Context

Schema change in 8e2bd74 added an optional paymentRail field to ExternalAccountDestinationReference, allowing users to specify which payment rail (ACH, WIRE, RTP, FEDNOW, etc.) to use when making transfer-out requests. This PR documents that capability.

Areas Reviewed (No Changes Needed)

• Kotlin sample app: No transfer-out tests exist; external account and quote tests remain correct
• Grid Visualizer: Code generator outputs valid requests (paymentRail is optional)
• transaction-lifecycle.mdx: Minimal example kept simple since page focuses on lifecycle, not all options

🤖 Generated with Claude Code

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[greptile-apps]

Greptile Summary

This PR documents the new optional paymentRail field on ExternalAccountDestinationReference by adding it to the transfer-out cURL examples in both the main send-payment page and the same-currency snippet, along with a <Tip> callout explaining its usage.

• send-payment.mdx: cURL request updated and a descriptive tip added listing common rail values (ACH, WIRE, RTP, FEDNOW) and when to specify one.
• same-currency.mdx: same cURL update applied, but the accompanying <Tip> is shorter — it omits the valid-values list and when-to-use guidance that the main page includes, leaving users of the global-p2p page with less complete information.

Confidence Score: 4/5

Safe to merge — changes are documentation-only and correctly reflect the new optional paymentRail field.

Both files correctly document the new field with matching cURL examples. The only gap is that the snippet's Tip is less informative than the main page's, leaving developers who reach the global-p2p flow without the list of valid rail values and when-to-use context.

mintlify/snippets/sending/same-currency.mdx — the tip text should be expanded to match the more complete version in send-payment.mdx.

Important Files Changed

Filename	Overview
mintlify/payouts-and-b2b/payment-flow/send-payment.mdx	Adds paymentRail: ACH to the transfer-out cURL example and a well-worded Tip explaining the field is optional and listing common rail values.
mintlify/snippets/sending/same-currency.mdx	Adds paymentRail to the snippet cURL example and a truncated Tip that omits the valid-values list and when-to-use guidance present in the main page tip.

Sequence Diagram

sequenceDiagram
    participant Client
    participant GridAPI as Grid API
    participant Rail as Payment Rail (ACH/WIRE/RTP/etc.)

    Client->>GridAPI: "POST /transfer-out { destination: { accountId, paymentRail? }, amount }"
    Note over GridAPI: If paymentRail omitted, Grid selects default rail
    GridAPI-->>Client: "201 Created { id, status: PENDING }"
    GridAPI->>Rail: Route transfer via specified (or default) rail
    Rail-->>GridAPI: Settlement confirmation
    GridAPI-->>Client: Webhook: OUTGOING_PAYMENT.COMPLETED

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Prompt To Fix All With AI

Fix the following 1 code review issue. Work through them one at a time, proposing concise fixes.

---

### Issue 1 of 1
mintlify/snippets/sending/same-currency.mdx:40-42
The `<Tip>` in the snippet is more terse than the equivalent tip in `send-payment.mdx`, which additionally lists valid rail values and explains when to use them. Since this snippet is imported in `global-p2p/sending-receiving-payments/sending-payments.mdx`, users landing on that page receive less guidance than users reading `send-payment.mdx`. Aligning the two tips ensures consistent documentation coverage regardless of which page a developer reaches.

```suggestion
<Tip>
  The `paymentRail` field is optional. If omitted, Grid selects a default rail for the destination. Specify a rail (e.g., `ACH`, `WIRE`, `RTP`, `FEDNOW`) when you need to control which payment network processes the transfer.
</Tip>
```

_{Reviews (1): Last reviewed commit: "docs: document paymentRail option for tr..." | Re-trigger Greptile}

[greptile-apps]

The <Tip> in the snippet is more terse than the equivalent tip in send-payment.mdx, which additionally lists valid rail values and explains when to use them. Since this snippet is imported in global-p2p/sending-receiving-payments/sending-payments.mdx, users landing on that page receive less guidance than users reading send-payment.mdx. Aligning the two tips ensures consistent documentation coverage regardless of which page a developer reaches.

Suggested change

	<Tip>
	The `paymentRail` field is optional. If omitted, Grid selects a default rail for the destination.
	</Tip>
	<Tip>
	The `paymentRail` field is optional. If omitted, Grid selects a default rail for the destination. Specify a rail (e.g., `ACH`, `WIRE`, `RTP`, `FEDNOW`) when you need to control which payment network processes the transfer.
	</Tip>

Prompt To Fix With AI

This is a comment left during a code review.
Path: mintlify/snippets/sending/same-currency.mdx
Line: 40-42

Comment:
The `<Tip>` in the snippet is more terse than the equivalent tip in `send-payment.mdx`, which additionally lists valid rail values and explains when to use them. Since this snippet is imported in `global-p2p/sending-receiving-payments/sending-payments.mdx`, users landing on that page receive less guidance than users reading `send-payment.mdx`. Aligning the two tips ensures consistent documentation coverage regardless of which page a developer reaches.

```suggestion
<Tip>
  The `paymentRail` field is optional. If omitted, Grid selects a default rail for the destination. Specify a rail (e.g., `ACH`, `WIRE`, `RTP`, `FEDNOW`) when you need to control which payment network processes the transfer.
</Tip>
```

How can I resolve this? If you propose a fix, please make it concise.

Note: If this suggestion doesn't match your team's coding style, reply to this and let me know. I'll remember it for next time!