Isn't your subscription active?
This might cause the issue:
Exceeding clients
You have reached the maximum number of clients
Only a Premium subscription offers unlimited clients.
Using a specific feature
You try to use Quotes/Estimates or another feature with a lower subscription.
Take a look at our pricing and check if the feature is in your actual subscription.
Have you tried everything above and still no luck? Then...
... we weren't notified about your purchase
and in that case and depending where you bought the subscription:
Send us your Apple bill or a screenshot of your Apple subscription
Send us your Google Play Order with a GPA number
If you paid by bank transfer, send us your receipt