Google will not accept your ordinary Gmail password from another program. An App Password is a separate 16-character key you create yourself, for this tool only.
Turn on 2-Step Verification in your Google account — App Passwords do not exist without it. Open Google's App Passwords page (link below) and sign in again if asked. Give it a name — “jobflow” — and create it. Google shows a 16-character password in four blocks. Copy it. Paste it in the field above. Spaces make no difference. Open Google App Passwords No such option? Either 2-Step Verification is still off, or your account belongs to a company or school whose administrator has disabled App Passwords.
This is not your Gmail password. It only lets this tool send mail as you, and you can cancel it at any moment from the same Google page.