As I know Fiverr balance is the primary method for gig promotion method. Is it the auto process to deduct the monthly amount from my balance?
Yep! However much money is spent on clicks from promoted gigs, that amount will be automatically taken from your Fiverr balance.
Fiverr also requests that you enter information for a backup payment option (like credit cards) so that in case you haven’t made any money on Fiverr, you can still pay for your promoted gig. Thanks!