The FCC allows alert texting (good information regarding a purchase) from a merchant’s nonautomated system to its existing customer. (https://transition.fcc.gov/cgb/consumerfacts/canspam.pdf).
In Europe rules regarding texting are more succinct. For most, the option of requiring a phone number on the check out page is enabled, noted by the red asterisk and a cell phones number preferred. The burden of proof regarding the consumer consent resides with the activity supplier. The activity supplier must prove that customer expressly and affirmatively provided consent. If the text opt-in box is pre-ticked, this can NOT be considered expressly and affirmatively providing consent. If the customer has to check to manually the box to opt-in, expressed consent is solved. TCPA violations are quite steep–$500 per text.
If your company opts to enable these boxes pre-checked on the internal interface, staff must be trained to ask the customer expressly and affirmatively for consent to send text messages.