If you purchased the Cloud Backup premium feature and it still appears to be disabled, it may just be that you haven't enabled a storage provider yet. Open the Squid settings, go to Backup and restore, then Cloud backup. Then tap on Storage providers and check the storage provider you want to enable (e.g. Dropbox, Box). After signing into the storage provider and going back to the cloud backup settings, you should be able to check Backup database and Export PDFs, which will enable the rest of the cloud backup settings.
If Storage providers is greyed out and tapping on it takes you to purchase the Cloud Backup premium feature, then your purchase has not been detected. See My premium features are missing! What happened? for help troubleshooting purchases.