Account quotas are provisioned in line with the current calendar month. If you sign up later in the month, both your quota and your cost is worked out on a pro-rata basis.
For example, if you sign up halfway through the month you will be allocated 50% of your bought-in messages, connections, and channels quota, and 50% of your rate limit allowances. You’ll also only pay 50% of the package cost.
A monthly Self-Service package of 6 million messages and 500 peak channels and connections, costing $19.99, would, therefore, generate a $9.99 invoice and a quota of 3 million messages and 250 peak channels and connections. At the start of the next month, you’d be charged the full amount, and receive the full quota.