Hi @mleblanc,

I know it’s a tough experience to encounter this error.

There’s an ongoing investigation concerning with “importing custom invoice templates”-related issue. Our engineers is currently working on the appropriate means to fix it. 

I’d recommend contacting our Support Team so you’ll be added as one of the affected user. You’ll then be notified with the updates on our progress. 

If there’s anything else you need, feel free to post again.