New Account Registration and Checkout Generate "error"

Hi,
I have installed OpenCart 3 on the following sub-domain for testing purposes. Things are working fine so far except that the New Account Registration and Checkout generate an "error". The pop-up window just shows "error" and nothing else.
So far I have tried:
- Disabling SEO URLs (thinking sub-domain may be the issue)
- Disabling email confirmations (thinking maybe SMTP info is not correct)

One more thing, right after the installation OpenCart asked me to move my storage folder out of Root, so I accepted this option and moved it one level above the root. I mean now the storage folder and public_html folder are at the same level.

Here's the store address:
https://totalmedical.000webhostapp.com

Could be API settings in the admin?

One more thing, right after the installation OpenCart asked me to move my storage folder out of Root, so I accepted this option and moved it one level above the root. I mean now the storage folder and public_html folder are at the same level.

No error / server access logs results posted. No full OC version posted. As for the storage folder options, see this post: viewtopic.php?f=176&p=733002#p717782

Sorry about the delay, the issue was resolved once I changed the SMTP settings from a public email service to my hosting email service.