How to add sixth camera for 1.99/month?

[TANDJ2009]

I have an Arlo Pro base station purchased with 4 cameras. Having decided we needed more I could see that I could have up to five free, but on the website it seemed that if I paid the 7.99 monthly subscription, I could then add a sixth camera for 1.99/month (I am in the UK). Having purchased two additional cameras, and signed up for the free trial of the subscription service, I cannot see how to add the sixth camera. This is where I read the info about the smart plans: https://www.arlo.com/uk/landing/arloSmart/default.aspx. 

Is it possible to add a sixth camera? How do I do it? Thanks

[Streak2]

Once you had added the subscription service then login as you usually would and select add new device and follow the on screen prompts.