Localstack insert default port in external uri

I charge via sam local the cloudformation. One lambda call a external mock in for example “aa.com/transfer”. The url i send via environment in the cloudformation. After the creation of lambda, I found that in the environment say “aa.com:4566/transfer”. Localstack via samlocal insert the port used by localstack. Why? If i force port in 80, it change to “4566/:80/transfer”!!