National Revenue Agency number

I assume you are French? If so after you move then apply for your residency card which will give you or Payroll the relevant number. There is no particular rush to do so.

Thanks for your reply.
I am French yes.
Isn't the residency card something different ? At the moment I need this number to be able to start work under probation...
I'll check this info.

Thanks again !

If you're already in process of moving to Sofia, then it might be sensible to focus on getting your residence permit sorted out first.

This is not a massively long process, it can be done in 2-3 business days at the Immigration Office.

As an EU citizen you need:

- proof of BG residence (rental contract in Sofia)
- proof of medical cover (your French EHIC card, or a Bulgarian "Health Insurance for Foreigners" policy, approx. 80 euros
- proof of finance (declaration + debit card or BG bank account) OR proof of job (employment contract)

Supporting documents not in Bulgarian need a legalized translation from a BG registered/certified translator. However, I believe they accept all passports without translation.

The Residence Permit has an identity number on it, and this is the number used by tax and social security office. I also had to go to the social security office and fill out a form to "activate" my number for social security payments.

As an EU citizen you are allowed to live and work in Bulgaria, even without completing any formalities. But if your company insists that you have to have the BG ID number, then I guess you have to get it.

I would have expected your company to have a been a bit more explicit about clarifying what you need and how you get it. If they're just palming you off on NRA that seems pretty unhelpful.