Went back on the link and here are the Terms and Conditions....
MileagePlus® mile offer terms and conditions
Each traveler is eligible for 30,000 MileagePlus miles. Miles are limited to one deposit per person. Each traveler must have their own MileagePlus account to claim the miles. All miles are subject to the MileagePlus program terms and conditions, included below. MileagePlus miles must be claimed by August 31, 2023.
Only original recipients of a communication from United about this offer (and other individuals traveling on the same reservation) are eligible. Offer is not transferable to any other individual. Eligibility will be determined by United in its sole discretion, and such determinations shall be final. Offer subject to change.
MileagePlus® terms and conditions
For the full terms and conditions of the MileagePlus program, visit https://www.united.com/ual/en/us/fly...lus/rules.html