Or worse-yet, opt-in means "Hey our rates are going up, but not if you agree to this" (something comcast did recently).
Or opt-in is stored in some database somewhere and might "accidentally be misread" due to a "bug".
If they want real-opt-in then it should be a SMS message at the time they want to know, and a phone-number you can reach out to for more information. This would give an audit trail at the very least.