Hi,
If you have done all the checks given in the thread like Master Data Maintainance, All the required checks in PIRs and POs
1. ERS ticked in vendor master
2. tax code maintained in PIR/PO
3. NO ERS should not be ticked in PIR
for Invoice Plan > maintain a condition record.
Go to TCODE > NACR
select condition type > INS
select key combination as needed > company code
maintain the condition record and then run MRIS.