Checkbox validation in PHP

### 1. Add the `required` attribute to the checkbox inputs in PHP (optional):
This ensures that browsers will perform basic client-side validation.

<input class="gfield-choice-input" name="services[]" type="checkbox" value="<?php echo esc_html($pc->term_id) ?>" id="choice_<?php echo esc_html($pc->term_id) ?>" aria-describedby="gfield_description_4_9" required>

However, this only applies basic validation in some browsers. To implement a custom validation that works across all browsers, you'll need to use JavaScript.

### 2. Add JavaScript for custom validation:
You can write a custom script to check if at least one checkbox is checked before the form is submitted. Here’s an example:

<script>
  document.addEventListener('submit', function(event) {
    // Find all checkboxes with the name 'services[]'
    var checkboxes = document.querySelectorAll('input[name="services[]"]');
    var isChecked = false;

    // Loop through all checkboxes and check if any of them is checked
    checkboxes.forEach(function(checkbox) {
      if (checkbox.checked) {
        isChecked = true;
      }
    });

    // If no checkbox is checked, prevent form submission and show an error
    if (!isChecked) {
      event.preventDefault(); // Prevent form submission
      alert('Please select at least one service category.'); // Show a message
    }
  });
</script>

### 3. Explanation:
– The JavaScript code listens for the form submission event.
– It checks if any of the checkboxes with the name `services[]` is checked.
– If none are checked, it prevents the form from being submitted and displays an alert to the user.
– If at least one checkbox is checked, the form can be submitted as usual.

### 4. (Optional) Add CSS for better user feedback:
You can also visually highlight the checkboxes or label if none are selected:

.gchoice {
  color: red; /* Optional: Make the text red or add a border to indicate an error */
}

This will ensure your form performs proper validation and provides feedback to users when they try to submit it without selecting any checkboxes.