What does the error message "Heroku Build Error: Unable to load xmlsec-openssl library" mean?

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The error message "Heroku Build Error: Unable to load xmlsec-openssl library" indicates that the Heroku app is unable to load the xmlsec-openssl library. This library is required in order to use certain functionality within the app. This error may be caused by a variety of issues, such as a missing or improperly installed library, incorrect configuration settings, or other environmental issues on the Heroku platform. In order to resolve this error, it may be necessary to troubleshoot the specific issue and take appropriate steps to fix it.