Answer
The passport must be valid on the date documents are submitted; some requirements and practical guidance also call for at least one year of remaining validity. Therefore, it is safest not to apply with a passport that will expire soon.
The passport is required to identify the applicant and confirm citizenship. Its details must match those in the other documents: first name, surname, date of birth, and citizenship. If the passport number changes while the case is being processed, the information will have to be updated.
If the passport is close to expiring, it is better to consider renewing it before applying. Formally, what matters is that the document is valid, but having at least one year remaining reduces the risk that the passport will expire during appointment scheduling, waiting, additional requests, or the processing of subsequent documents.