There are not enough free numbers available in the number interval

What causes this issue?

Line item documents are written for the combination of ledger, version,
company code or global company and fiscal year which you have planned.
You have changed or created so many records that more than 999 records
have been posted, and therefore several document numbers must be used.
For this reason, there are not enough free document numbers available.

System Response

The system issues an error message and will not allow you to continue with this transaction until the error is resolved.

How to fix this error?

Extend the number interval using the number range maintenance
transactions.

Error message extract from SAP system. Copyright SAP SE.