Hi
I hope this may able to help you, You have make changes for serial number profile that you are using.
1. Goto T-Code SPRO -->Plant Maintenance and Customer Service->Master Data in Plant Maintenance and Customer Service
2. Click on Technical Objects --> Serial Number Management
3. Define Serial number profiles, then select the serial number that you are using, then double click on the serializing procedures
4. Then for MMSL Procedure Change the Serial Usage --SerUsage indicator value from 2 to 3.
If you are required to make serial number created first, then you can also check the indicator ExistReq for given serial number profile.
Indicator: Serial Number Existence Requirement
Indicator that determines whether the serial numbers entered for a business transaction need to be created first as a master record in the system.
Use
If the indicator is set, the serial numbers must be created first as a master record in the system.
If the indicator is not set, the serial numbers are created during a business transaction.
Try to verify the same creating PO then performing the MIGO
Thanks,
Jagdeep