What's the biggest mistake you've done?

Hello Warriors. I wanted to make a thread about mistakes you've done providing online services to your clients.

I've recently made the mistake of accidentally making a typo on a client's e-mail on a website. This is pretty bad based on the fact that I'm also running a PPC campaign for them. Fortunately, only $25 dollars has been used in the PPC campaign, so it's not that big of a deal.

I haven't fessed up to my mistake to my client yet, but I will call him tomorrow and I will apologize and reimburse him the $25 dollars used for the clicks. I'm going to do this because I also got a letter wrong on the contact forms, so if anyone has tried to contact him, they obviously weren't capable of sending a message.

I'm aware of the fact that people make mistakes, but I'm definitely not looking forward to calling him and telling him this. It's going to make me look pretty bad, but I'll just man up.

Let me know what mistakes you've done and what you have done to repair them!