/cart with only cached data (cache_time=-1)
The /cart endpoint supported cache_time for a long time, allowing developers to hit the Two Tap cache instead of the supplier sites, allowing for faster response times. However, even with a large cache_time, if a product was out of stock, Two Tap would hit the retailer site to double check.
To ensure consistency, cache_time has been extended to support cache only responses. Just send the value as -1.