"FeatureNotAvailable" "The requested feature is not available" in Sandbox

Hello,

I am getting error during API of send message using the username : +13612607320

Content: {

"errorCode" : "FeatureNotAvailable",

"message" : "The requested feature is not available",

"errors" : [ {

"errorCode" : "MSG-242",

"message" : "The requested feature is not available"

} ]

}
Please let me know, how to fix this issue.

Thanks