A billing cycle is a period during which a user subscribes to a said plan. The credit associated with the plan is usable during the billing cycle and lapses at the end of the billing cycle.
Billing cycle spans for 30 days from the date of activation. For instance, if a user subscribes to $65 plan on 1st March, 300K credits are allocated to the user's account and are available to the user till the end of a billing cycle, i.e. 30th March. On 31st March, a new billing cycle begins, and credits are updated.
In case of plan upgrade, the user subscribes to the new plan immediately, and the billing cycle starts from that date.
Updated about 3 years ago