You can try this Regex Example:
^[a-zA-Z]*$
This regular expression allows only Latin letters in the field and nothing else.

In December, the Signify product team released another update, and we're excited to share it with you!
Validation rules have been added to the fields in the document. The following fields come with predefined fields:

Text Field Validation
For individual text fields, you can define the minimum and maximum number of characters or digits required.
If you need to set a validation rule that isn’t available by default on the platform, you can use a custom regex. In this case, don’t forget to provide a hint text to ensure the rules are clear to the recipient.

You can try this Regex Example:
^[a-zA-Z]*$
This regular expression allows only Latin letters in the field and nothing else.
Validation for Checkboxes
You can specify how many options the recipient is allowed to select. For example, you can define that the recipient must select at least 1 and at most 3 checkboxes.
Numeric Field
A new field type, "Number," has been added, allowing you to set minimum and maximum values during validation.
Date Field
Validation now includes the option to specify whether the input should be a past or future date.
From now on, you no longer need to send a document to yourself just to see how it will appear to the recipient.
With the Preview Function, you can review the document before sending it and go through exactly the same steps the recipient will experience.

You can select any recipient, including during bulk send.

If you've been using SMS for two-factor authentication on the portal, you can now add an authentication app as well.
This feature is especially useful if you’re in a place where receiving SMS is challenging. You can easily and securely access the system using a code generated in an authenticator app.

You can activate this feature on your own profile, or if you're an admin, you can make it mandatory for all users.

The system will block your profile for 5 minutes if five consecutive incorrect attempts to enter your password and two-factor authentication code are detected.
You will also receive an email notification about this.
If you're using the Enterprise plan, you’ve previously been able to see details about your user's document sending activities and other actions.
In the new release, you can now also view additional details such as the time of login, IP address, browser, and other information.
If you have any questions about the new functionality or want to give it a try, our team is always here to help. Feel free to contact us.
Our team will get in touch with you shortly