Here is how your IAX config file(s) should look. You should forward your buy virtual number using the "Your own VOIP Server" option and use your Asterisk IP in the "Host" .

 iax.conf:
[buyonline-iax-1]
type=user
permit=46.19.209.42
context=from-buyvirt 
 [buyonline-iax-2]
type=user
permit=46.19.210.42
context=from-buyvirt