Hello @JuliaB043 ,
We're sorry to hear you weren't able to submit the contacts. Did you check them all to ensure the email addresses were 100% validly typed out (no misspellings or missing characters such as the @ or . )?
In the future, I'd recommend using the upload from file way of uploading contacts if you're going to be uploading a large number at a time, or using the copy/paste multiple in smaller batches to minimize lost work if you run into formatting errors or connectivity issues.