1) Upgrade to any paid subscription plan
This will give you an opportunity to buy Traffic Analytics API package and get an API key.

2) Buy package that suits your needs
Go to the bottom of Subscription info page, choose your plan, and click Get access +10k units.
Traffic Analytics API comes in all paid subscriptions in 2 plans:
- Basic: provides only traffic summary data
- Extended: provides traffic summary data and extended information about the website traffic
The monthly limit rate included by default is 10,000 requests. This API does not use any API units.
You can always upgrade your plan from Basic to Extended or increase your limits by choosing the corresponding option on the Subscription info.

3) Get your API key
After the purchase is made you’ll receive your API key via customer support specialist.