No, it has nothing to do with the “processing” status of a payment. The order was placed successfully and you have activated your account. The Alarm.com account is active, it just needs to see that communication from the panel in order to be accessible.
The panel must communicate with Alarm.com first before you will be able to login. There is no other hurdle or consideration at this time.
To troubleshoot the issue with cellular signaling, first reboot your panel. Settings > Advanced Settings > Reboot panel.
Wait about 5 minutes after boot up, then try another cell test. If no success, connect the panel to wifi and update the firmware via the steps below before trying another cell test: