This is something I found with MDM ABAP APIs and thought to share. It will be quite old and small thing for experts but I guess still a little good for starters.
1. The *Table code* is case sensitive in MDM ABAP API. If you add *CUSTOMERS* in your console, please use *CUSTOMERS* only in the ABAP API program. Please do not use *Customers* or *customers. Another example is *Customer_MDM* , so dont use *Customer_mdm* etc.*
Works - Only Code of Table is case-sensitive: not Table Name.
Not Works - Code needs to be exact, its case-sensitive.
2. The User-ID is always capital since ECC uses caps for user-Id. Please use *MDMUSER* as console and not *mdmuser. *mdmuser* will give exception that *User is not found.**
Works - Only Name of User is case-sensitive! 
Not Works - Name needs to be in capital letters, its case-sensitive.
Same is true for Table Fields as well.
In the end, its also a tip that Please Use the ABAP API How to Guides provided. I must admit that they are really helpful and even helped me in solving a simple customer requirement. Cheers !
