diff --git a/ios/epac/Data/Adapters/BillsService.swift b/ios/epac/Data/Adapters/BillsService.swift
index b8a35a11..900634a0 100644
--- a/ios/epac/Data/Adapters/BillsService.swift
+++ b/ios/epac/Data/Adapters/BillsService.swift
@@ -96,8 +96,21 @@ struct BillsService {
         guard let legisURL = URL(string: "\(legisInfoBase)/\(billSlug)")
             ?? URL(string: legisInfoBase) else { return nil }
 
+        // Backend bill-depth routes (versions, diff, committee, amendments,
+        // lobbying, PBO) are keyed by the numeric LEGISinfo id, not the display
+        // bill number. Carry that id in Bill.id so those calls resolve; keep
+        // Bill.number as the display value. Fall back to the number only when
+        // LEGISinfo omits a usable id, which leaves backend depth unavailable
+        // rather than mis-keyed.
+        let legisInfoID: String
+        if let billID = raw.BillId, billID > 0 {
+            legisInfoID = String(billID)
+        } else {
+            legisInfoID = number
+        }
+
         return Bill(
-            id: number,
+            id: legisInfoID,
             number: number,
             title: title,
             sponsorName: raw.SponsorEn ?? "",
@@ -236,6 +249,7 @@ private struct BillStageSpec {
 /// Mirrors the JSON object returned by the LEGISinfo bills endpoint.
 /// Only the fields we use are decoded; unknown fields are ignored.
 private struct LEGISinfoBill: Decodable {
+    let BillId: Int?
     let BillNumberFormatted: String
     let LongTitleEn: String?
     let ShortTitleEn: String?
diff --git a/ios/epac/Model/Bill.swift b/ios/epac/Model/Bill.swift
index 08632cf8..68232077 100644
--- a/ios/epac/Model/Bill.swift
+++ b/ios/epac/Model/Bill.swift
@@ -14,8 +14,8 @@ import SwiftUI
 // MARK: - Bill
 
 struct Bill: Identifiable, Codable, Sendable {
-    let id: String          // bill number e.g. "C-50", "S-12"
-    let number: String      // same as id
+    let id: String          // numeric LEGISinfo id e.g. "13608745"; backend bill-depth key
+    let number: String      // display bill number e.g. "C-50", "S-12"
     let title: String
     let sponsorName: String
     let status: BillStatus
diff --git a/ios/epacTests/BillsServiceTests.swift b/ios/epacTests/BillsServiceTests.swift
new file mode 100644
index 00000000..93b90ac8
--- /dev/null
+++ b/ios/epacTests/BillsServiceTests.swift
@@ -0,0 +1,162 @@
+@testable import epac
+import Foundation
+import Testing
+
+/// Mapping tests for `BillsService`, the LEGISinfo → `Bill` boundary.
+///
+/// The bill-depth backend (versions, diff, committee, amendments, lobbying,
+/// PBO) is keyed by the numeric LEGISinfo id, not the display bill number, so
+/// `Bill.id` must carry that numeric id while `Bill.number` stays the display
+/// value. Regression coverage for EPAC-2307.
+@Suite(.serialized)
+struct BillsServiceTests {
+    @Test func billMappingUsesNumericLegisInfoIdAsBillId() async throws {
+        let harness = try makeHarness()
+        defer { harness.cleanup() }
+        defer { BillsServiceMockURLProtocol.requestHandler = nil }
+
+        BillsServiceMockURLProtocol.requestHandler = { request in
+            (
+                HTTPURLResponse(
+                    url: try #require(request.url),
+                    statusCode: 200,
+                    httpVersion: nil,
+                    headerFields: ["Content-Type": "application/json"]
+                )!,
+                Self.legisInfoJSON()
+            )
+        }
+
+        let bills = try await BillsService.fetchBills(parliament: 45, session: 1, network: harness.service)
+        let bill = try #require(bills.first { $0.number == "C-11" })
+
+        // Backend bill-depth key — must be the numeric LEGISinfo id, not "C-11".
+        #expect(bill.id == "13608745")
+        #expect(bill.number == "C-11")
+    }
+
+    @Test func billMappingFallsBackToNumberWhenLegisInfoIdMissingOrZero() async throws {
+        let harness = try makeHarness()
+        defer { harness.cleanup() }
+        defer { BillsServiceMockURLProtocol.requestHandler = nil }
+
+        BillsServiceMockURLProtocol.requestHandler = { request in
+            (
+                HTTPURLResponse(
+                    url: try #require(request.url),
+                    statusCode: 200,
+                    httpVersion: nil,
+                    headerFields: ["Content-Type": "application/json"]
+                )!,
+                Self.legisInfoJSON()
+            )
+        }
+
+        let bills = try await BillsService.fetchBills(parliament: 45, session: 1, network: harness.service)
+
+        // BillId absent entirely → fall back to the display number.
+        let missing = try #require(bills.first { $0.number == "S-12" })
+        #expect(missing.id == "S-12")
+
+        // BillId present but not a usable id (<= 0) → fall back to the number.
+        let zero = try #require(bills.first { $0.number == "C-99" })
+        #expect(zero.id == "C-99")
+    }
+
+    // MARK: - Fixtures
+
+    /// Minimal LEGISinfo JSON array exercising the three id cases the mapping
+    /// must handle: a numeric id, an absent id, and a non-usable (<= 0) id.
+    private static func legisInfoJSON() -> Data {
+        Data(
+            """
+            [
+              {
+                "BillId": 13608745,
+                "BillNumberFormatted": "C-11",
+                "ShortTitleEn": "An Act respecting example data",
+                "ParliamentNumber": 45,
+                "SessionNumber": 1
+              },
+              {
+                "BillNumberFormatted": "S-12",
+                "ShortTitleEn": "An Act respecting senate example data",
+                "ParliamentNumber": 45,
+                "SessionNumber": 1
+              },
+              {
+                "BillId": 0,
+                "BillNumberFormatted": "C-99",
+                "ShortTitleEn": "An Act respecting zero-id example data",
+                "ParliamentNumber": 45,
+                "SessionNumber": 1
+              }
+            ]
+            """.utf8
+        )
+    }
+
+    private func makeHarness() throws -> BillsServiceNetworkHarness {
+        let configuration = URLSessionConfiguration.ephemeral
+        configuration.protocolClasses = [BillsServiceMockURLProtocol.self]
+        let session = URLSession(configuration: configuration)
+
+        let suiteName = "BillsServiceTests.\(UUID().uuidString)"
+        let userDefaults = try #require(UserDefaults(suiteName: suiteName))
+        userDefaults.removePersistentDomain(forName: suiteName)
+
+        let cacheDirectory = FileManager.default.temporaryDirectory
+            .appendingPathComponent("BillsServiceTests-\(UUID().uuidString)", isDirectory: true)
+        let cacheStore = HTTPResponseCacheStore(userDefaults: userDefaults, cacheDirectory: cacheDirectory)
+
+        return BillsServiceNetworkHarness(
+            service: NetworkService(session: session, cacheStore: cacheStore),
+            userDefaultsSuiteName: suiteName,
+            cacheDirectory: cacheDirectory
+        )
+    }
+}
+
+private struct BillsServiceNetworkHarness {
+    let service: NetworkService
+    let userDefaultsSuiteName: String
+    let cacheDirectory: URL
+
+    func cleanup() {
+        UserDefaults.standard.removePersistentDomain(forName: userDefaultsSuiteName)
+        try? FileManager.default.removeItem(at: cacheDirectory)
+    }
+}
+
+private enum BillsServiceMockURLProtocolError: Error {
+    case missingHandler
+}
+
+private final class BillsServiceMockURLProtocol: URLProtocol {
+    nonisolated(unsafe) static var requestHandler: ((URLRequest) throws -> (HTTPURLResponse, Data))?
+
+    override class func canInit(with request: URLRequest) -> Bool {
+        true
+    }
+
+    override class func canonicalRequest(for request: URLRequest) -> URLRequest {
+        request
+    }
+
+    override func startLoading() {
+        do {
+            guard let handler = Self.requestHandler else {
+                throw BillsServiceMockURLProtocolError.missingHandler
+            }
+
+            let (response, data) = try handler(request)
+            client?.urlProtocol(self, didReceive: response, cacheStoragePolicy: .notAllowed)
+            client?.urlProtocol(self, didLoad: data)
+            client?.urlProtocolDidFinishLoading(self)
+        } catch {
+            client?.urlProtocol(self, didFailWithError: error)
+        }
+    }
+
+    override func stopLoading() {}
+}