Swift.DecodingError.dataCorrupted and app crash with "The given data was not valid JSON.", underlyingError: Optional(Error Code=3840 "No value"

here is my code

struct ServerMessage: Codable { let error, email, firstname, lastname: String let Id: Int }

out of 5 variables returned from api, 4 are string and 1 is int,

class HttpAuth: ObservableObject { var didChange = PassthroughSubject<HttpAuth, Never>()

var authenticated = false {
    didSet {
        didChange.send(self)
    }
}

func checkDetails(useremail:String, userpass: String) {
    guard let url: URL = URL(string: "http://www.mytestdomain.com/webapi/Users.php") else {
        print("invalid login URL")
        return
    }
    
    var urlRequest: URLRequest = URLRequest(url: url)
    urlRequest.httpMethod = "POST"
    urlRequest.setValue("application/json", forHTTPHeaderField: "Content-Type")
    do {
        let params = ["action": "login", "UserEmail": useremail, "UserPass": userpass]
        urlRequest.httpBody = try JSONSerialization.data(withJSONObject: params, options: .init())
        
        URLSession.shared.dataTask(with: urlRequest) { (data, resp, err) in
            
            guard let data = data else { return }
            
            let finalData = try! JSONDecoder().decode([ServerMessage].self, from: data)
            
            print(finalData)
            
            if let err = err {
                print("Failed to login: ", err)
            }
            print("Login Sucess")
        }.resume()
        
    } catch {
        print("Failed to get data", error)
    }
}

}

and this is the output of my php based web api

{"error":"false","Id":1,"email":"emailidatmaildotcom","firstname":"somename","lastname":"lastname"}

i double checked the api using postman.

i am getting this error 2021-07-29 19:44:00.378908+0530 kapp[4536:146582] [] nw_protocol_get_quic_image_block_invoke dlopen libquic failed app/login.swift:79: Fatal error: 'try!' expression unexpectedly raised an error: Swift.DecodingError.dataCorrupted(Swift.DecodingError.Context(codingPath: [], debugDescription: "The given data was not valid JSON.", underlyingError: Optional(Error Domain=NSCocoaErrorDomain Code=3840 "No value." UserInfo={NSDebugDescription=No value.}))) 2021-07-29 19:44:02.613900+0530 kapp[4536:145289] kapp/login.swift:79: Fatal error: 'try!' expression unexpectedly raised an error: Swift.DecodingError.dataCorrupted(Swift.DecodingError.Context(codingPath: [], debugDescription: "The given data was not valid JSON.", underlyingError: Optional(Error Domain=NSCocoaErrorDomain Code=3840 "No value." UserInfo={NSDebugDescription=No value.}))) (lldb) edit: once the app is crashed, decode is showing this error also Thread 12: EXC_BAD_INSTRUCTION (code=EXC_I386_INVOP, subcode=0x0)

the api is written using php, any help is appreciated, thanks.