Prestashop: "An error occurred while sending the message."

I am using PrestaShop 1.7 with its default theme. I also have contact form module installed.

But when I try to send a message from the "contact us page" using the contact form created by the contact form module.

It throws the error below :

An error occurred while sending the message, please try again.

How can I fix this?

I have just figured out the problem.

Actually, I'd tried to upgrade my shop to 1.7.3.1 when the notification first popped up. Then somehow the installation went wrong but the module I was using, which was 1-Click Upgrade, was saying something like "don't worry we will recover to the version that you were using before.".

Well, they didn't! And I hadn't thought this could be the problem at first.

Then I started thinking about which file or files could have possibly been changed. Using an online file compare tool I saw that contactform.php in /modules/contactform was different than the one I was using before.

After changing that file to the older one the problem was solved!

If that file was not the case for you I recommend you to try other files if you'd tried to upgrade the version to the newer one and failed during the process just like me.

Hope this helps people having the same issue without having to think about for days like me.