Question4:

A taxpayer is booking an expenditure on Provisional Basis in the month of March-18 . The said Expenditure is covered under RCM Liablity . Now please tell whether the liablity to pay GST will arise in the month of March 18 or at the month when bill is received by taxpayer .

Answer:

In GST liability to pay tax arises at the time of supply (Section 12 or Section 13). We understand that you are making provision for inward supply of service (like advocate fees etc). 
According to Section 13 (3),  In case of reverse charge  liability to pay tax arises earlier of  date of payment or date immediately following 60 days from the date of issue of invoice
But proviso to this  section  specifies that where it is not possible to determine the time of supply under above then the time of supply shall be the date of entry in the books of account of the recipient of supply.  
Now the phrase ====where it is not possible to determine the time of supply under above then ===  requires high  interpretation and debate
In normal course it  is never possible that the date of payment or provision of service both are not available because it is possible only when no records or books are maintained At this point of time we are talking about registered person because reverse charge applies to him Now if a person is registered then section 35 with relevant rules (Rule 56 to rule 58) apply to him so he has to keep records If he  is require to keep records then a provision in law assuming that he is not keeping records can't be framedUnder these circumstances   it seems that this proviso is added for the present  situation like cases
Accordingly we are of the view that tax should be charged 
We will welcome if you have different view for discussion  (Reply dt. 16/4/2018)