What are the steps to send sales order custom field from CRM to ECC

Hi Xperts,

We have created a custom field in sales order [ VBAK] and successfully replicate its value from ECC to CRM. But while doing the enhancement to replicate the field value from CRM to ECC [ When the SO is created in CRM ] we are not able to do so.

We used a FM in CRM0_300, but while replicating the SO from CRM to R/3 it is not getting called.

Please help us by providing the steps to do the full enhancement to replicate the custom field of SO from CRM to ECC.

Thanks in Advance.