Defining a Margin on Web API gives “Bad Request” about zxing HOT 3 CLOSED

You will need to url-encode the pipe character in URLs generally, I believe, and that's the same here. Use %7C and there is no error

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I imagine the old chart server code is technically wrong to allow this character without escaping, but general servlet engines enforce it. See for example.https://itecnote.com/tecnote/tomcat-how-to-make-apache-tomcat-8-0-41-to-allow-the-pipe-character-in-url-get-request/

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Thanks for the solution and again all your work!

Although it's kind of unintuitive you have to do that, science the Google API accepts the request unsing the pipe char:
https://chart.googleapis.com/chart?chs=230x230&cht=qr&chld=h|1&chl=123456789

from zxing.