# Description
Add `addCustomUserFieldValidationCallback` to the user fields validation mixin. This allows you to add a custom validation when checking the validity of custom user field values in the signup form on submit.
```js
addCustomUserFieldValidationCallback((userField) => {
if (userField.field.name === "my custom user field" && userField.value === "foo") {
return EmberObject.create({
failed: true,
reason: I18n.t("value_can_not_be_foo"),
element: userField.field.element,
});
}
});
```
In the case your custom validation deems an input value `failed`, you return an EmberObject with the fields `failed: true`, `reason`, and `element`.
```js
return EmberObject.create({
failed: true,
reason: I18n.t("value_can_not_be_foo"),
element: userField.field.element,
});
```
which will then display your custom `reason` to the user attached to the given user custom field input and will not submit the signup form.
<img width="288" alt="Screenshot 2024-06-06 at 11 08 40 AM" src="https://github.com/discourse/discourse/assets/50783505/11168fb8-8806-43f0-9417-73991bbd1178">
# Other
- Add `addCustomUserFieldValidationCallback` to the plugin api
- Bump plugin api version
- Update plugin api changelog
- Add tests
69193c4bd5