Sending invitations by SMS / text message through EventCreate is not supported due to spam laws and restrictions.
If you need to invite people by text message, you should invite guests via personal phone by sharing your event URL. To find your URL, go into your Event Dashboard > Setup > Website > URL
Once a guest has registered for your event and granted permission to be contacted by text, you can send event reminders and updates through EventCreate.
Note: Direct text messaging is only available for phone numbers based in US States and Canadian Provinces at this time.