The phrase "a required purchase" is correct and usable in written English.
It can be used when referring to a purchase that is necessary or mandatory for a specific purpose or situation.
Example: "To access the premium features of the software, a required purchase of the subscription plan is necessary."
Alternatives: "an essential buy" or "a mandatory acquisition".
Given the paucity of Wii U releases at the moment, it goes without saying that this is a required purchase for those who have ventured onto Nintendo's eccentric new platform; whether you are looking for an adventure that you can enjoy alone as a seasoned gamer or with children who will marvel at a Lego town brought to functioning, animated life, it will entertain for days.
With every new track, it's clear that this is a required purchase for serious Stones fans, and a great introduction for younger ones.
If you have a coupon that has a required purchase amount, give that one first.
The book was reviewed in the Library Journal and received a coveted star, calling it "exceptional advice", "a required purchase" and stated "well done..."...
Shelvey failed to get the required purchase on a pull-back, while Sterling was denied when his shot was deflected high off the sliding Steven Taylor.
I ended up in touch with somebody at the Strand, and they offered me a complimentary pass to the talk (attendance required purchasing a $20 Strand gift card, or a copy of To Wit).
Upgrading that piece will require purchase of a new Shield Controller, which is a $60 cost; still better than buying a new Shield at $200.
Other options include charging much higher co-pays and/or requiring purchase at a narrow network of restricted pharmacies.
From that point on, playing an entire track or replaying the song will require purchasing a "music pass".
Also, while a traditional storage setup requires purchasing servers and the storage network separately, the move to cloud erases this problem.
Torrentfreak asked one VPN provider and found that the reason for that is simply that passing all that traffic requires purchasing a certain amount of dedicated bandwidth.
