Welcome to the community!
It sounds like the phone number you were trying to text might have been a landline. While sending text messages to mobile numbers is included in many plans, sending texts to a landline (home phone) is a 3rd party (TeleMessage) service which incurs additional cost (25¢). If you would like to prevent sending texts to a landline, you would have to contact TeleMessage (firstname.lastname@example.org) directly and ask them to disable the service for your number.
Hope this helps 😀