Resolution:
If we are ready to make changes to the RFC

1) Remove the parameters of LINE Data Type from Import tab
2) Define the same parameters under Tables tab.
3) Save the RFC and activate it.
4) Do a refresh schema in the Designer Project
5) Try running the adapter & BW process

If we do not want to do any changes in the RFC, we can use the following work around suggested by SAP Support.

Write a custom RFC function module wrapper that converts such (InterTable which appear in Import/Export Parameter) parameters to TABLES and EXTERNAL application calls this wrapper over RFC API. Here the advantage is, you do not need to change SAP standard BAPIs/RFCs.

Also there is some performance implication with RFC enabled module with Internal Table as Import/Export Parameter. Please find the below note from SAP Support on this.

"Generally, we discourage users from using Internal Table type as Import/Export parameter type in a RFC enabled function module:- it is slow comparing to using TABLES"