403 when installing private app Cannot connect to proxy

I am trying to write an app for the marketplace. I have an app descriptor that points to a AWS API gateway.

When I try to add app by submitting a link to the app descriptor JSON file using “Install app from URL” …/workspace/settings/addon-management I enter this:

https://s3.eu-west-2.amazonaws.com/codereview.doctor/bitbucket-staging.json

when I submit the first step works OK. I click “grant access” but then I get error:

problem installing the app. The app failed to be installed: Error calling installed at URL <the_url>: HTTPSConnectionPool(host=’<the_host>’, port=443): Max retries exceeded with url: /default/bitbucket-events/ (Caused by ProxyError(‘Cannot connect to proxy.’, error(‘Tunnel connection failed: 403 Forbidden’,)))

However according to my server logs no request is being made to the API gateway URL

Is this a known problem?

If I manually do a POST request to the endpoint specified in the app descriptor then I get a 200 response.

Oddly if I add a proxy (beeceptor) so baseUrl" is set to and that url just proxies the API gatweay url then everything works.

bitbucket worked as soon as I changed my endpoint from eu-east-1 to any other region