Currently long text replication is not supported by standard for BP to BP data exchange. This has been addressed in note 548003 - Data exchange of long texts.
If you want to replicate the long text for BP and BP, you could consider to activate the CVI in ECC system or implement a Z module or exit for the same .
Long text replication between CRM BP and S/4 HANA.
In S/4 HANA system, the long text replication will not be supported for BP to BP as well as Customer master/ Vendor Master. This is because the implementation in ECC the receiving application is BP and Customer Master/ Vendor Master is updated by BP, hence long text replication will not be supported in any situation in such scenario. i.e. BP to BP or BP to CM or BP to VM or vice versa.
Long text replication between CRM BP and ECC vendor.
Please implement the following note, including the manual steps and the coding correction.
This note can add the object 'LFA1' into the selection condition of PITX.
Then please also map the text ID between CRM and ECC in tcode PITX.
Sales area text replication between CRM BP and ECC customer.
The sales area based text is also not supported in standard. According to the CRM BP data model, maintenance of Sales Area-dependent text objects is not possible. In CRM BP we do not maintain long text at sales area level, therefore these texts are not exchanged between ECC customer and CRM BP. You can also check in transaction PITX. Only the object 'KNA1' is offered and not 'KNVV'. For KNVV there are no corresponding texts in CRM.
However, you can explicitly transfer the texts using the following exits:
In R/3 you can use the exits DE_BCS2S for manipulating the BAPIMTCS and use DE_EIOUT to manipulate the complex structures.
In CRM, you can use the middleware exits SMOUTIL3 for mapping into CRM. Also refer to the note 417906 for additional information.
More blogs about the data exchange between CRM and ECC, please refer to the following links. I hope they could help you more.