There is an htaccess in x-payments by default.
Uncomment the IP of your server.
This is built into x-payments by default.
Code:
# Uncomment the lines below to allow access to the admin script
# only from specific IP-addresses
# (replace 192.168.10.32 below to your IP-addresses)
# Uncomment the lines below to allow access to the api script
# only from specific IP-addresses
# (replace 192.168.10.32 below to your IP-addresses)
If you do this, there is no need to do a robots.txt because IP blocking will prevent anyone that is not you or your server from seeing the files.