diff --git a/Libraries/Sources/APIService/Protocols/Service.swift b/Libraries/Sources/APIService/Protocols/Service.swift
new file mode 100644
index 0000000..0f559f3
--- /dev/null
+++ b/Libraries/Sources/APIService/Protocols/Service.swift
@@ -0,0 +1,30 @@
+//
+//  Service.swift
+//  APIService
+//
+//  Created by Javier Cicchelli on 04/12/2022.
+//  Copyright © 2022 Röck+Cöde. All rights reserved.
+//
+
+import Foundation
+
+public protocol Service {
+    func getUser(credentials: Credentials) async throws -> Me
+    func getItems(id: String, credentials: Credentials) async throws -> [Item]
+    func getData(id: String, credentials: Credentials) async throws -> Data
+    func createFolder(id: String, name: String, credentials: Credentials) async throws -> Item
+    func uploadFile(id: String, file: File, credentials: Credentials) async throws -> Item
+    func deleteItem(id: String, credentials: Credentials) async throws
+}
+
+// MARK: - Structs
+
+public struct Credentials {
+    let username: String
+    let password: String
+}
+
+public struct File {
+    let name: String
+    let data: Data
+}
diff --git a/Libraries/Sources/APIService/Structs/APIClient.swift b/Libraries/Sources/APIService/Structs/APIClient.swift
index ca7c67f..2295426 100644
--- a/Libraries/Sources/APIService/Structs/APIClient.swift
+++ b/Libraries/Sources/APIService/Structs/APIClient.swift
@@ -49,7 +49,7 @@ extension APIClient: Client {
         case .noContent:
             throw APIClientError.notSupported
         case .badRequest:
-            throw APIClientError.itemAlreadyExist
+            throw APIClientError.itemNameInvalidOrDefined
         case .unauthorized,
              .forbidden:
             throw APIClientError.authenticationFailed
@@ -114,7 +114,7 @@ public enum APIClientError: Error {
     case responseNotReturned
     case authenticationFailed
     case itemIsNotFile
-    case itemAlreadyExist
+    case itemNameInvalidOrDefined
     case itemDoesNotExist
     case notSupported
 }
diff --git a/Libraries/Tests/APIServiceTests/Cases/Structs/APIClient+RequestTests.swift b/Libraries/Tests/APIServiceTests/Cases/Structs/APIClient+RequestTests.swift
index 40851f0..0949ea0 100644
--- a/Libraries/Tests/APIServiceTests/Cases/Structs/APIClient+RequestTests.swift
+++ b/Libraries/Tests/APIServiceTests/Cases/Structs/APIClient+RequestTests.swift
@@ -35,6 +35,10 @@ final class APIClientRequestTests: XCTestCase {
         client = .init(configuration: sessionConfiguration)
     }
     
+    override func tearDown() async throws {
+        client = nil
+    }
+    
     // MARK: Request cases
     
     func test_withSomeEndpoint_andSomeModel_whenResponseStatusOk() async throws {
@@ -150,7 +154,7 @@ final class APIClientRequestTests: XCTestCase {
         // WHEN & THEN
         do {
             _ = try await client.request(endpoint: endpoint, model: Me.self)
-        } catch APIClientError.itemAlreadyExist {
+        } catch APIClientError.itemNameInvalidOrDefined {
             XCTAssertTrue(true)
         } catch {
             XCTAssertTrue(false)