Hi,
FEBA is not used for importing lockbox files. Use T-code FLB2 for uploading lockbox and FLB1 for post processing function.
Here accounting entry will be
Lock Box Clearing account
To Bank Clearing account
And
Bank Clearing Account
To Customer account
Once you upload EBS(Electronic Bank Statement) file into SAP then entry will be as below.
Main bank account
To Lock Box clearing account
Regards,
Mohammed