Customer was automatically unsubscribed and now I can't send them an invoice or email

[VazuVases]

A customer who purchased a few things from me about a month ago, has now placed a larger order. I went to email them an answer to their question, and was given a message both through my Square app and my business email, that they've unsubscribed and I can no longer send emails to them. I was able to reach them through my personal email and ask them if they changed anything, and they said no they hadn't. We're both stumped and have no idea why this happened, and how we can continue our correspondence through the business email, since it's blocked. I'm trying to invoice them for their next purchase, and the system won't let me do that either. 

Any thoughts or suggestions? 

Thanks.

[Kassi_]

Hey there, @VazuVases - 

Sorry to hear you're having issues getting in touch with your customer via email. Are they able to add your email address to their "Safe List" on their end? 

Whenever you're trying to email them, is it through your email provider? Or where were you seeing the error message about your customer unsubscribing?

I will keep an eye out for your reply👀.