how to use server IP address to perform a GET request

I am using a ftp server (say A) and in there, I created a php file with javascript fetch request to another server (say B). Now the criteria of B is, I have to whitelist the IP address from where the request is taken, so I have whitelisted the A’s server IP address but when I try doing the fetch request. It looks like the fetch request is taking my own public IP address rather than the A’s IP address and thereby I am getting 403 error!

therefore, I want to ask is there any way to make sure the fetch request uses the ftp server’s IP address (i.e. the A), rather than my system’s public IP address?