Offer 41k euros/year non negotiable atm (with pto, bonus, some other perks) before taxes. Probably there will be better career opportunities then my current location 

I have been working with this company as freelancer for 2 years with 28k/year working for 80 hours/week (because company had tough times so long working hours were required to achieve results). Now they want me to move to Germany (Munich) as regular employee because they say "You have done so much for the company (essentially helped to tackle all problems achieving exceptional  results and saving many customers for the company)"

Role Data Scientist, ML and DL engineer. 

Current salary 28k euros/ year no PTO, no bonus, no raises  ( honestly two times got 49 euro with taxes as bonuses on achieving 100% Accuracy in production environment (impossible task though))

On 28k I don't pay taxes except  some international money transfer fee which is about 10% and living expenses are 500 euro/month 

I have two options accept the offer or Ask for raise in current salary and don't move.