E-mails won't send

Hello guys! I’m testing the [free] plug-in on this site https://veionamala.com/loja/kit-fitas-adesivas-chevron/

I received only one e-mail on my tests, but now I can’t seem to receive anymore. I’m wondering if there is something I’m missing.

I’m sending it manually on the single product page, but I never receive the e-mails. Can you please help me? Is there anything I need to configure?

https://wordpress.org/plugins/yith-woocommerce-waiting-list/