fetch - How to access GitHub Enterprise

In an internal Plugin I want to upload svgs from Figma to Github.

With Github.com that works fine, however, to make it work with our Github Enterprise account I have trouble.

To check if the plugin can even connect to GitHub Enterprise, I use this reduced code:

 

However, I get the error notification “Failed to connect to GitHub Enterprise API”.

Our GitHub enterprise is internal, accessible behind a VPN. I am running FIGMA with the plugin code from within the VPN, but I am thinking that this call I do might still come “from outside” and therefore cannot access the internally GitHub Enterprise?