First enable debug/trace for webADI. This will help you to easily identify the problem.
Possible fixes :
- When Interface type is chosen as "API - Procedure" then only procedure calls should be used in the name, functions cannot be used .
Package XX_ABC
Package body XX_ABC_PROC
XX_ABC_FUNC
Correct definition
Interface Type --> API - Procedure
Package Name --> XX_ABC
Procedure/Function Name --> XX_ABC_PROC
Wrong definition
Interface Type --> API - Procedure
Package Name --> XX_ABC
Procedure/Function Name --> XX_ABC_FUNC
And for "API - Function" vice versa.
2. API Returns in the Interface definition should be set to "FND Message Code".