Well if they ask for that then it's necessary. Nothing scary in it, just send them your driver license or something like that.
You must be careful sending your id, and take precautions (eg ID-fraud)
- Only provide the information which are relevant.
- Mask details which are unnecessary to know (eg your social security number).
- Describe on the copy of your ID: It is a copy, the date, the reason of the copy
In the Netherlands you have guidelines from the authorities how to copy your ID in a safe way:
https://www.rijksoverheid.nl/onderwerpen/identiteitsfraude/vraag-en-antwoord/fraude-voorkomen-met-kopie-id-bewijsI am sure other countries have the same guidelines, check it first before you copy and send your ID!