Second request failed (socket hang up)

I’m using a remote webservice to generate a token with a basic authentification.

When I send my request throught postman the first time it works, but whenever I try to send it again I get the following error “Error: socket hang up”.
If I close and restart postman it works again, but only one time.
If I juste wait for like 5 minutes it also works again.

I guess postman keep something alive with the server but I don’t now how to fix that.
I tried adding a “Connection: close” instead of the default “Connexion: keep-alive” but it does not fix the issue.

I searched the web for this issue but I did not find anyone with the issue except the one that proposed the header Connexion solution.

Here is the output of the console of three tests (the first one working).