cannot receive verification code

cannot receive verification code by through messages when trying to add another phone number to my Apple ID.

can receive phone calls to & from both numbers but not messages to & from both.

only one phone number is able to send & receive.

when trying to set up apple id with the secondary number it sends verification code to the secondary number that cant receive text messages.

why cant i get the verification code via a phone call, similar to setting up password & security