Issue while perfoming HTTP callout: Unable to tunnel through proxy. Proxy returns "HTTP/1.1 500 Internal Server Error"

Question

I've created a class with a method that performs an HTTP call to an external system. The system received and send data in XML.

When I execute this code to call my web service from an Anonymous Window:

RA_GTSCheckService.performCheck('S119440');

I get this error message:

Unable to tunnel through proxy. Proxy returns "HTTP/1.1 500 Internal Server Error"

Issue while perfoming HTTP callout: Unable to tunnel through proxy. Proxy returns

What I've tried:

Add the host in a remote site setting. With or without security enabled, the error appears.
Test the same request in Postman. In postman it works without problems, but from Salesforce the problem appears

This is my apex class:

You can read it at this link:

Oct 30 10:31 AM - Codeshare

I've searched for information about this issue but didn't find anything useful. If anyone has an idea about how to fix it, please comment it here.

Thank you!

#Salesforce Developer

Sushil Kumar · Accepted Answer

@Juan E. Martinez https://trailblazers.salesforce.com/profileView?u=0053A00000ECsTwQAL  This is most likely related to firewall blocking your request. Is this some internally hosted api? You may need to work with your network team to allow access.

Juan E. Martinez · Answer

Hi  @Sushil Kumar https://trailblazers.salesforce.com/profileView?u=0053000000CTbv8AAD  thanks for your response. Yes, your assumption was correct, this is a internal API of my company, and the problem was not in Salesforce nor inside my code, but instead in the API it self so I had to talk with the team in charge of that API.    I'll leave here all the details about how I managed to work around this issue, in case that it helps someone. In fact a couple of folks have written me on LinkedIn asking me how I fixed it.    Basically this issue wasn't caused by my code in Salesforce, or the way in which I was calling the API    This issue in my case was caused by the API itself    I realized that the API that I was calling was an internal API of the company, and that API was not open to receive connections from the public internet, So I had to ask the Team in charge of it to make it public to receive calls     In my case, I was connected through a company laptop, which was connected to the company's VPN    if I used postman in this laptop, it worked, but if I used Postman from another laptop, I got the error    What happens is that the API was only open to receive connections through this VPN,  so that's what I mean when I say that the API wasn't public , it was private and restricted to connect only in this way, by using the company's VPN      Since the Salesforce servers live in the cloud,  Salesforce doesn't have any VPN to connect, and therefore we see this issue   To solve it I had to talk with the team that was in charge of the API and ask them to make it available from the public internet, not just the one that used the VPN    that was my case, chances are that you're doing everything right in your code, but the API is not published yet

Issue while perfoming HTTP callout: Unable to tunnel through proxy. Proxy returns "HTTP/1.1 500 Internal Server Error"

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