how to detect if there is any bug in website and improve site performance

Hi,

Can someone help me - how can i be sure that there is BUGS or NO BUG in my website?

The reason i am asking this cause in last few weeks i am getting FB messages from advertising peoples that there is a bug in my website which causing bad performance. But for me website is working as normal, apart from less sale.

Also, last night i have launched a campaign on FB (new ads on FB), and todays morning i noticed an unbelievable visitors between 2am-4am and then nothing at all. Seems like something not correct. How can i get that many visitors i never had before, in one same time?

Can someone tells me what i am missing here and how i can be sure that nothing wrong or is something wrong than how to fix that? store url : https//: deshoeshop. com

Thanks.

You can use GTM to track every JS errors that appears on the site[https://support.google.com/tagmanager/answer/7679411?hl=en#:~:text=Google%20Tag%20Manager’s%20JavaScript%20error,variable%20when%20a%20tag%20fires.].