You can paste up to a maximum of 1,000 Urls at a time depending on the usage allowance for the plan you're on.
When uploading in large batches, it may take additional time to process everything, and you may need to wait a little while before you can add more coverage. Once you've hit the import button you can get on with other things while we work on your import!
If you have any issues with adding coverage please contact us via the messenger when signed in or via email.