error code

Check with your carrier?

Answers posted over at the AT&T forums for message 6 us01lv range from the receiving number having had a call-protection feature enabled, to a problem with Wi-Fi assist, to a spam caller.

https://forums.att.com/conversations/data-messaging-features-internet-tethering/message-6-for-1-specific-phone-number/5defd1d0bad5f2f606f42063

https://forums.att.com/conversations/samsung/message-6-us-01lv/5defd050bad5f2f606d8060a

https://forums.att.com/conversations/apple/us01lv-message/5defda6ebad5f2f6068cd1cd

https://forums.att.com/conversations/apple/cannot-call-certain-phone-numbers-error-message/5defe4f2bad5f2f60648fa6b