High compliance is required by law in the USA and Canada.
It means your customer must double opt in their agreement to receive texts from you.
The goal is to ensure the text communication channel is kept 'clean' and free from spam and unsolicited messages.
Customers who double opt in to receive your text messages agree that they really want to hear from you via text and value your text communications.
If you are currently on a lower level compliance you may choose to turn to a higher level of compliance.
Click the link for more information on How to Turn to a Higher Compliance.