The phrase "request basis" means that something will only be provided or done when asked or requested for. It means you have to make a request for it before it can happen or be provided. Full definition
In the time it takes to handle the illegal access, the speculative execution has the contents accessed and can make requests based on the data that affect the cache. (zdnet.com)
Our 2 Bedroom Apartments offer one bathroom in most rooms with some offering two bathrooms, they are available on request basis only and can not be guaranteed. (mantrahotels.com)
Our custom blends are on a customer request basis. (botanicals.com)