I'm just unable to receive a refresh_token when creating a successfull Oauth authentication with Gmail (for sending with SMTP)

Response:
{
"access_token": "ya29.a0..pX7akJmlStQUtrxVeHGX2Mi9sakaWezHax0spWec9QV4A0179",
"expires_in": 3593,
https://mail.google.com/ ",
"token_type": "Bearer",
"id_token": "eyJhbGci..._l2hfOAg"
}

Could it be something related to that App is still not reviewed?

I've added &access_type=offline as its mentioned in the documentation with no luck.

Thanks.

Just added:

authUri += '&access_type=offline';
authUri += '&prompt=consent';

At the end of the URL when opening the Oauth screen.

please try to use

&prompt=login