Since OTP 21,
ssl:ssl_accept/2: deprecated; use ssl:handshake/2 instead
a little bit of explanation about this change can be found here
it's only a warning during compilation, but it's you use warning_as_error for production mode, it might be a problem;
handshake method not exist before OTP 21, it's not very easy to switch to this version.
do you have roadmap to take all compatibility with OTP 21 ?