When Gmail is configured to use Okta as SSO solution, the "Send Mail" block in QAA cannot be used with their smtp.
This is a current product limitation. At the moment we only support Gmail via a standard Google password or via an app password. Use of Gmail with external single sign on solutions is currently not supported.
Qlik has previously received feedback on this feature. For up to date information and to express your interest in this feature, review https://community.qlik.com/t5/Suggest-an-Idea/Qlik-Application-Automation-add-support-for-quot-Gmail...