Appearing Custom field inputs in MIRO item level (BAdI mrm_item_custfields)

Hi Experts,

I apologize if I have not followed other thread helps and the question is repeated. 

I followed the below thread to implement the custom tab in the MIRO item level except I left or not done the append fields to RSEG table. Remaining of all the steps provided in the link are covered. 

https://www.sapyard.com/steps-to-add-custom-tab-in-standard-miro-item-screen-using-badi-mrm_item_custfields/

Other than my screen inputs all other values are appearing (in t_drseg_custom TYPE tdrseg_cust ). I can see my fields are there in the debugging screen but values are not passed. 

Please help me  where did I miss and how to fix this? Many thanks. 

Note: The append structure is added to RSEG table with the new fields as same as in CI_DRSEG.

Even though all the mappings are done as provided in the above link and I can see the values are passing but I cannot see inside the FM ‘MRM_INVOICE_DOCUMENT_POST’. 

T_DRSEG is not having the values to the new field.  Where it was missed or is it any standard SAP issue that need to look. 

I would be grateful if anyone answer to this with a suitable solution.

Thanks for your time here.