You have to bet the $500 before you get the bonus. So bet $500 and cover it elsewhere for a minimal lose!
If you want to be safe, after depositing the bonus call them and ask “hey where is my bonus?!” They will tell you that you have to bet the $500 first. Always good getting confirmation from them in case your first $500 bet wins and account fattens up (they may be like hey your from an ineligible states etc..)
People have had issues with neds before so bet with caution. Don’t turn the bonus over then try withdraw – leave it in the account for a bit.