Query regarding RCM

For RCM one has to prepare Self Invoice , who pay tax on reverse charge , same you have to file in GSTR1 and will be reflected in GSTR2A /2B ,after reflection you can claim credit .

Agree with Prasad

Practically self invoice is not available it is theoretical only meaning by if you put your GSTN in your GSTR1 system doesn't accept it, thus practically we are claiming ITC in the month we pay RCM.

Ignore prompt on liability for inward supplies attracting reverse charge in Table-3.1 (d)”  as said by CBIC
It is noticed that the system is giving alert when the taxpayer revises the auto-populated values upward by 10% in table 3.1(d) which pertains to inward supplies attracting reverse charge. This alert is erroneous. The technical team is working to resolve the same at the earliest.
Meanwhile, the taxpayers may kindly continue to declare their correct liability in Table-3.1(d) pertaining to liability on inward supplies attracting reverse charge and proceed to file GSTR-3B

Yes you can claim itc in the same month