Register Supplier Issue Invoice without GST for Taxable Supply

Nitesh (Ipcc both group) (60 Points)

04 August 2021  
Interior Design Service received from Registered Person. He has issued Invoice without charging GST for Supply of Design Service and Interior Materials like sofa chairs etc.

Can this bill be treated as inclusive of GST ?

Is person liable to charges GST forgets to charge on bill, can he recover later on?

Will this expense bill in Service receiver book be treated as valid documentary proof to book the expenses?