Antivirus alarm when my client clicks the link to the upload webpages.
(AVAST: it stopped the connection of URL:TechScam because it affected upbox.me)

Very strange, first time I hear about that but thanks for letting me know! I'm checking on Google what this means and will do my best to add a fix accordingly!

Actually, I've checked and I have found that it does not come from my app / website but from your client's computer that is infected with the "TechScam" virus. The Avast popup is probably showing up when they access your box URL because they need to pick some files on their computer (there is a file picker) which triggers the alert to show up. It's described here : https://howtofix.guide/url-techscam/#What_does_the_pop-up_with_URL_TechScam_detection_mean. They probably need to run a virus analytics on their computer with Avast to clean it but it has no relation with my website (my website is not infecting anything).

Let me know if I can help further!

Thanks,
Axel