The main problems during customizing data download
All the customizing data download need to be done using the R3AC3 adapter object. The main problem that could fail the download is missing entries in R3 table CRMATAB. eg. if you're to download DNL_CUST_KTOKD - account group, the relevant table T077D and T077X must exist in CRMATAB on ERP.
If this table doesn't contain the necessary entries for your customizing download to work, you can either manually maintain this table or use report SMOF_FILL_CRMATAB.
If you choose to use this report, you run this report in CRM to fill this R3 table.
When you run this report, you need to fill in the following parameter:
Source Site Name --- R3 system site
Objectname ----- the adapter object
(if table CRMATAB is empty and you want to fill in entries for all the adapter objects, you can also check the checkbox 'All objects'.)