How to resolve :thymeleaf.exceptions.TemplateInputException: (template: "class path resource [templates/unlock.html]")

Question

this is my htmpl page where I got an error: unlock.html

<p th:text="${successMsg}" class="text-success">

    <p th:text="${errorMsg}" class="text-danger">

    <form th:action="@{/unlock}" th:object="${unlock}" th:method="POST">

        <div class="form-outline mb-6">
            <h6>Your Email :<p th:text="${unlock.email}"/> </h6>
            <input type="hidden" th:field="${unlock.email}"/>
        </div>

        <div class="form-outline mb-4">
        <input type="password" id="form2Example22" class="form-control" th:field="*{tempPwd}"/>
        <label class="form-label" for="form2Example22">Temporary Password</label>
        </div>

        <div class="form-outline mb-4">
            <input type="password" id="form2Example23"
                class="form-control" th:field="*{newPwd}"/> 
                <label class="form-label" for="form2Example23">New Password</label>
        </div>
        
        <div class="form-outline mb-4">
            <input type="password" id="form2Example24"
                class="form-control" th:field="*{confPwd}"/> 
                <label class="form-label" for="form2Example24">Confirm Password</label>
        </div>

        <div class="text-center pt-1 mb-5 pb-1">
            <input type="submit" value="unlock" class="btn btn-primary btn-block fa-lg gradient-custom-2 mb-3"/>
        </div> </form>

This is controller:

@GetMapping("/unlock")
    public String unlockPage(@RequestParam String email, Model model) {
        
        UnlockForm unlockFormObj = new UnlockForm();
        unlockFormObj.setEmail(email);
        
        model.addAttribute("unlock",unlockFormObj);
        
        return "unlock";
    }
    
    @PostMapping("/unlock")
    public String unlockUserAccount(@ModelAttribute("unlock)") UnlockForm unlock, Model model) {

        //validate user entered password and current password should same
        if (unlock.getNewPwd().equals(unlock.getConfPwd())){

            //if valid then unlock the account
            boolean status = studentService.unlockAccount(unlock);

            if (status){
                model.addAttribute("successMsg", "Your account unlocked successfully..");
            }else {

                model.addAttribute("errorMsg","Given temporary password is incorrect, check email once..");
            }
        }else {

            //if not valid then send error msg as response to the client
            model.addAttribute("errMsg", "New Password and Confirm password must be same");
        }

        System.out.println(unlock);

        return "unlock";
    }

Data correctly store in the database but as response message not sending to UI.

I was trying to unlock the user account by clicking the link which was received in my email.

When I inserting the temp password and entering new password, It will be stored in the database but success message not going as response to UI.

The error is coming:

org.thymeleaf.exceptions.TemplateInputException: An error happened during template parsing (template: "class path resource [templates/unlock.html]")
    org.thymeleaf.templateparser.markup.AbstractMarkupTemplateParser.parse(AbstractMarkupTemplateParser.java:241)
    org.thymeleaf.templateparser.markup.AbstractMarkupTemplateParser.parseStandalone(AbstractMarkupTemplateParser.java:100)
    org.thymeleaf.engine.TemplateManager.parseAndProcess(TemplateManager.java:666)
    org.thymeleaf.TemplateEngine.process(TemplateEngine.java:1098)
    org.thymeleaf.TemplateEngine.process(TemplateEngine.java:1072)
    org.thymeleaf.spring5.view.ThymeleafView.renderFragment(ThymeleafView.java:366)
    org.thymeleaf.spring5.view.ThymeleafView.render(ThymeleafView.java:190)
    org.springframework.web.servlet.DispatcherServlet.render(DispatcherServlet.java:1406)
    org.springframework.web.servlet.DispatcherServlet.processDispatchResult(DispatcherServlet.java:1150)
    org.springframework.web.servlet.DispatcherServlet.doDispatch(DispatcherServlet.java:1089)
    org.springframework.web.servlet.DispatcherServlet.doService(DispatcherServlet.java:965)
    org.springframework.web.servlet.FrameworkServlet.processRequest(FrameworkServlet.java:1006)
    org.springframework.web.servlet.FrameworkServlet.doPost(FrameworkServlet.java:909)
    javax.servlet.http.HttpServlet.service(HttpServlet.java:555)
    org.springframework.web.servlet.FrameworkServlet.service(FrameworkServlet.java:883)
    javax.servlet.http.HttpServlet.service(HttpServlet.java:623)
    org.apache.tomcat.websocket.server.WsFilter.doFilter(WsFilter.java:51)
    org.springframework.web.filter.RequestContextFilter.doFilterInternal(RequestContextFilter.java:100)
    org.springframework.web.filter.OncePerRequestFilter.doFilter(OncePerRequestFilter.java:117)
    org.springframework.web.filter.FormContentFilter.doFilterInternal(FormContentFilter.java:93)
    org.springframework.web.filter.OncePerRequestFilter.doFilter(OncePerRequestFilter.java:117)
    org.springframework.web.filter.CharacterEncodingFilter.doFilterInternal(CharacterEncodingFilter.java:201)
    org.springframework.web.filter.OncePerRequestFilter.doFilter(OncePerRequestFilter.java:117)