The phrase "additionally purchase" is correct and usable in written English.
It can be used when suggesting that someone should buy something extra or in addition to what they are already considering.
Example: "If you're interested in the premium package, you can additionally purchase a one-year subscription for a discounted rate."
Alternatives: "also buy" or "further acquire".
Additionally, purchasing a diamond smaller than one carat can be significantly less expensive as prices rise steeply at every whole carat weight.
The Hitachi executives additionally purchased 500 of the massager-shaped chocolates which were given out at the company's sales conference that year.
BRD9092 and BRD56491 were additionally purchased from ChemDiv, and BRD5459 was purchased from Sigma.
Moreover if all the additionally purchased calories were consumed the net effect on health, balancing the beneficial effects (e.g. reduction in cardiovascular disease) with the adverse consequences from weight gain may be neutral or even negative [ 14].
Additionally, the purchase bolsters Hodder Headline's literary ambitions.
Additionally, each purchase of a Nike+ device like a FuelBand, for example—is a further financial and psychological investment in the ecosystem.
Additionally, that purchase is even more likely to happen if the product is easy to see and easy to buy (i.e. directly within your audiences' social media feeds, and attached to a seamless purchasing interface).
Additionally, the purchase of the reagents needed for building and screening one library by traditional protocol will supply sufficient reagents for ten or more libraries applied by enrichment protocol.
Additionally, Defendant purchased misspelled keywords from other search engines besides Google, for which Defendant paid approximately $0.96.
Additionally, MicroVentures purchases shares on secondary markets — not just early-stage startups.
Additionally, Stern purchased employee David Vargas a house, a car and a cell phone, Scott claims in her statement".
