Hello Andrey,

I found an unwanted result during testing on sandbox account and i also shared it with support team.
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{status:Duplicate TNs detected:[2029884658, 2029884659, 2029884665, 2029884667, 2029884691, 2029884693, 2029884699, 2029884704, 2029905628, 2029905675],statusCode:413}
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I made some big changes in current code, please monitor the behaviour of new code and give your feedback.
Sorry, but you may loose your number if the code doesn’t work. However i have old code and will make as it was.

The Current code worked on sandbox and mail was also not repeating the number.