ITC Not Auto-Populating in GSTR-3B Despite Ledger Balance

I have ₹902 balance in Electronic Credit Ledger (March ₹456 + April ₹446) but GSTR-3B for May 2025 only shows ₹333.05 ITC from GSTR-2B.

When I try to manually enter ₹1,235.05 (902+333.05), system shows error:

"Input tax credit values are at variance with auto-populated data in table 4A. Upward variance is in contravention to Rule 36(4) of CGST Rules, 2017."

Questions:

1. Why doesn't previous months' unused ITC appear in current GSTR-3B?
2. How to utilize the ₹902 accumulated credit from March/April?
3. Will this amount expire if not used, and when?
4. Is this a system limitation or correct interpretation of Rule 36(4)?

Current Status:

• Electronic Credit Ledger: ₹902 balance
• May GSTR-2B: ₹333.05 ITC available
• GSTR-3B allows only ₹333.05, not full ₹1,235.05

Any guidance on proper utilization of accumulated ITC would be appreciated.

Thanks in advance!