Zend certified PHP/Magento developer

Magento 2 Mageplaza SMTP module error

I have a problem with this module: https://marketplace.magento.com/mageplaza-module-smtp.html

Everytime I click on Test Now (send a test email), it throws me the following error

enter image description here

I have read tons of problems and all of them says that you need to download the latest core module, I did that and did not work either.
The exception.log and system.log have no errors about this, report folder neither.

The weird thing is that I have this module (older version) installed in other shops, and is working perfectly, but if I try to move the module to this store, it does not let me to activate the module, the Save Config button gets disabled.

I want to install this new version of smtp and core.

Thanks!