diff --git a/InterlinedList/Services/APIClient.swift b/InterlinedList/Services/APIClient.swift
index 2749cac..b2bfa86 100644
--- a/InterlinedList/Services/APIClient.swift
+++ b/InterlinedList/Services/APIClient.swift
@@ -169,10 +169,26 @@ final class APIClient {
         return response.identities ?? []
     }
 
-    func unlinkIdentity(provider: String, providerId: String) async throws {
-        struct Body: Encodable { let provider: String; let providerId: String }
-        try await deleteCamel("/api/user/identities", body: Body(provider: provider, providerId: providerId))
-    }
+    /// `DELETE /api/user/identities?provider=…` — the route reads `provider` from
+    /// the **query string** and never parses a body, so a JSON payload here answers
+    /// `400 "provider is required"`. It also deletes by `{userId, provider}` alone,
+    /// which removes *every* identity stored under that provider value (an account
+    /// with two rows for the same provider loses both); the identity's own id is
+    /// not read at all.
+    func unlinkIdentity(provider: String) async throws {
+        let encoded = provider.addingPercentEncoding(withAllowedCharacters: Self.queryValueAllowed) ?? provider
+        try await delete("/api/user/identities?provider=\(encoded)")
+    }
+
+    /// `.urlQueryAllowed` permits the sub-delimiters `+ & = ? # /` — legal
+    /// *somewhere* in a query string, but inside a single value they end it or
+    /// split it into another parameter. `+` matters most: the backend reads params
+    /// through `URLSearchParams`, which decodes a literal `+` as a space.
+    private static let queryValueAllowed: CharacterSet = {
+        var allowed = CharacterSet.urlQueryAllowed
+        allowed.remove(charactersIn: "+&=?#/")
+        return allowed
+    }()
 
     /// Actively verifies a stored OAuth credential — the only route that reports real
     /// token health. The five `/status` routes report whether a *provider* is
diff --git a/InterlinedList/Services/APIClientTransport.swift b/InterlinedList/Services/APIClientTransport.swift
index 43fb7ee..02e8678 100644
--- a/InterlinedList/Services/APIClientTransport.swift
+++ b/InterlinedList/Services/APIClientTransport.swift
@@ -135,8 +135,9 @@ extension APIClient {
         return try decoder.decode(T.self, from: data)
     }
 
-    /// DELETE with a camelCase JSON body — a few routes identify their target in
-    /// the body rather than the path (identity unlink, push unregister).
+    /// DELETE with a camelCase JSON body — for routes that identify their target in
+    /// the body rather than the path (push unregister). Check the route first: a
+    /// body sent to a route that reads the query string is silently ignored.
     func deleteCamel<B: Encodable>(_ path: String, body: B) async throws {
         var request = try jsonRequest(path, method: "DELETE")
         request.httpBody = try camelCaseEncoder.encode(body)
diff --git a/InterlinedList/Views/LinkedIdentitiesView.swift b/InterlinedList/Views/LinkedIdentitiesView.swift
index 074500a..a869c63 100644
--- a/InterlinedList/Views/LinkedIdentitiesView.swift
+++ b/InterlinedList/Views/LinkedIdentitiesView.swift
@@ -272,7 +272,7 @@ struct LinkedIdentitiesView: View {
         errorMessage = nil
         pendingUnlink = nil
         do {
-            try await APIClient.shared.unlinkIdentity(provider: identity.provider, providerId: identity.id)
+            try await APIClient.shared.unlinkIdentity(provider: identity.provider)
             await load()
         } catch APIError.status(401) {
             authState.handleUnauthorized()
diff --git a/InterlinedListTests/APIClientTests/APIClientIdentitiesTests.swift b/InterlinedListTests/APIClientTests/APIClientIdentitiesTests.swift
index 80c7a77..01b22bf 100644
--- a/InterlinedListTests/APIClientTests/APIClientIdentitiesTests.swift
+++ b/InterlinedListTests/APIClientTests/APIClientIdentitiesTests.swift
@@ -65,33 +65,81 @@ final class APIClientIdentitiesTests: XCTestCase {
 
     // MARK: unlinkIdentity
 
-    func test_unlinkIdentity_sendsDeleteWithBody() async throws {
+    func test_unlinkIdentity_sendsDeleteToIdentitiesPath() async throws {
         session.stub(data: Data(), statusCode: 204)
-        try await sut.unlinkIdentity(provider: "github", providerId: "abc-123")
-        XCTAssertEqual(session.lastRequest?.url?.path, "/api/user/identities")
+        try await sut.unlinkIdentity(provider: "github")
         XCTAssertEqual(session.lastRequest?.httpMethod, "DELETE")
-        let body = String(data: session.lastRequest?.httpBody ?? Data(), encoding: .utf8) ?? ""
-        XCTAssertTrue(body.contains("\"provider\":\"github\""))
-        XCTAssertTrue(body.contains("\"providerId\":\"abc-123\""),
-                      "Body must use camelCase providerId. Got: \(body)")
+        XCTAssertEqual(session.lastRequest?.url?.path, "/api/user/identities")
+    }
+
+    func test_unlinkIdentity_sendsProviderAsQueryParameter() async throws {
+        session.stub(data: Data(), statusCode: 204)
+        try await sut.unlinkIdentity(provider: "github")
+        XCTAssertEqual(session.lastRequest?.url?.query, "provider=github")
+    }
+
+    func test_unlinkIdentity_sendsEmptyBody() async throws {
+        // The route reads the query string and never parses a body; a JSON payload
+        // here is what produced 400 "provider is required".
+        session.stub(data: Data(), statusCode: 204)
+        try await sut.unlinkIdentity(provider: "github")
+        XCTAssertNil(session.lastRequest?.httpBody)
+    }
+
+    func test_unlinkIdentity_mastodonProvider_keepsInstanceSuffix() async throws {
+        session.stub(data: Data(), statusCode: 204)
+        try await sut.unlinkIdentity(provider: "mastodon:techhub.social")
+        let value = URLComponents(url: try XCTUnwrap(session.lastRequest?.url), resolvingAgainstBaseURL: false)?
+            .queryItems?.first(where: { $0.name == "provider" })?.value
+        XCTAssertEqual(value, "mastodon:techhub.social")
+    }
+
+    func test_unlinkIdentity_providerWithQueryDelimiters_percentEncodesThem() async throws {
+        session.stub(data: Data(), statusCode: 204)
+        try await sut.unlinkIdentity(provider: "mastodon:a+b&c=d")
+        let query = try XCTUnwrap(session.lastRequest?.url?.query)
+        XCTAssertEqual(query, "provider=mastodon:a%2Bb%26c%3Dd")
+        let value = URLComponents(url: try XCTUnwrap(session.lastRequest?.url), resolvingAgainstBaseURL: false)?
+            .queryItems?.first(where: { $0.name == "provider" })?.value
+        XCTAssertEqual(value, "mastodon:a+b&c=d")
     }
 
     func test_unlinkIdentity_sendsBearerToken() async throws {
         session.stub(data: Data(), statusCode: 204)
-        try await sut.unlinkIdentity(provider: "github", providerId: "x")
+        try await sut.unlinkIdentity(provider: "github")
         XCTAssertEqual(session.lastRequest?.value(forHTTPHeaderField: "Authorization"), "Bearer tok")
     }
 
     func test_unlinkIdentity_403_throws() async throws {
         session.stub(data: Data(), statusCode: 403)
         do {
-            try await sut.unlinkIdentity(provider: "github", providerId: "x")
+            try await sut.unlinkIdentity(provider: "github")
             XCTFail("Expected throw")
         } catch APIError.status(let code) {
             XCTAssertEqual(code, 403)
         }
     }
 
+    func test_unlinkIdentity_401_throws() async throws {
+        session.stub(data: Data(), statusCode: 401)
+        do {
+            try await sut.unlinkIdentity(provider: "github")
+            XCTFail("Expected throw")
+        } catch APIError.status(let code) {
+            XCTAssertEqual(code, 401)
+        }
+    }
+
+    func test_unlinkIdentity_404_surfacesRouteMessage() async throws {
+        session.stub(json: #"{"error":"Identity not found"}"#, statusCode: 404)
+        do {
+            try await sut.unlinkIdentity(provider: "github")
+            XCTFail("Expected throw")
+        } catch APIError.server(let message) {
+            XCTAssertEqual(message, "Identity not found")
+        }
+    }
+
     // MARK: verifyIdentity
 
     func test_verifyIdentity_sendsCorrectPath() async throws {