Add a "special instructions" field to the checkout process (which is then saved to the order)
Install this module via composer:
composer require silvercommerce/checkout-special-instructions
Once installed, this module adds a textarea to the customer details form in the checkout process.
If this field has a value, it is transfered to the Estimate/Invoice, which can then be viewed by going to the "Sales" tab in the admin (a new field is added below the items ordered).
NOTE If you want to add the special instructions to any emails sent, you need to ensure you add the
$SpecialInstructions variable to your email templates.