Hello Arvind,
To your question,
1) You can stop the CIF queue in ECC & APO and ATP a Sales order. This will stop the CIF queue in ECC side (SMQ1). From there you can debug the process into APO.
2) I don't know if your BADI is correct. But you can also use /SAPAPO/RRP_SRC_EXIT BADI for your need.
Hope this helps.
Thanks,
Uthaman