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Did you receive an error of "Device Not Registered" when trying to activate your YouMail account?
Your device number is registered? Please ensure it's in the first SIM slot and that we have the appropriate permissions to read phone state.
The text that pops up should mention that ###-###-#### is not currently registered to your YouMail account.
What this means is your Sim card is giving off a different number than the account you are currently trying to activate.
To fix this you will need to add the number into your YouMail account and activate so your missed calls to your new number will be forwarded to YouMail.