SIM800L phone number format in AT+CMGS="520xxxxx7"

I have aSIM800L working with no errors. After AT+CMGS=“xxxxxxxxxx” and the text:
Hello World; and Terry24q too The response from SIM800L is:
+CMGS: 4
OK
However no text message ever reaches my inbox.
Should have plenty of power with an 18650 LiPo and 470 uF across power at SIM.
What format should the phone # be?