The primative trigger allowable in Power Automate only works sucessfully from a new email arrival in the gMail inbox. You have to have a gMail rule apply the label. The power automate has ZERO capability of allowing a developer to test this functionality unless you can generate the email manually, but if the email is from automation, then you need to be able to control that automation a force it to generate the email. Without a new email hitting the inbox, the power automate tools are useless.