Mandatory reporting of inter State supplies ensures accurate GSTR 3B/GSTR 1 disclosure and correct Input Tax Credit reversal accounting. Suppliers must report place of supply wise inter State supplies to unregistered persons, composition taxable persons and UIN holders in Table 3.2 of FORM GSTR 3B and corresponding GSTR 1 tables; maintain accurate customer state data; and ensure GSTR 1 amendments reflect in GSTR 3B. FORM GSTR 2B auto populates Table 4(A) of GSTR 3B with total ITC, but registered persons must separately report absolute ineligible reversals in Table 4(B)(1) and temporary/reclaimable reversals in Table 4(B)(2). Net ITC credited to the electronic credit ledger is 4(A) less 4(B)(1) and 4(B)(2); time barred ITC may be shown in Table 4(D)(2). Reversals under section 17(5) must be placed in Table 4(B), not Table 4(D).