2975506 - Cannot combine documents in app "Create Outbound Files"

When multiple billing documents are combined which includes a negative billing document in app" Create Outbound Files", the error occurred "Cannot combine documents".

• SAP S/4HANA Cloud

1. Open app"Create Outbound Files" 
2. Select these billing documents and then click "Combine"
3. The error "Cannot combine documents" pops up

1. In SSCUI 101922 "Define GTI Tax Invoice Keys", configured with "Not allowed to combine positive documents with negative ones" or "Combine positive and negative documents automatically" under Combine Flag
2. The negative billing document has no corresponding positive billing document (has no the same "Material" or no the same customer)
3. The negative billing document amount bigger than the positive billing document

Firstly, you need to check the configuration through SSCUI 101922 "Define GTI Tax Invoice Keys" and choose "Allowed to combine positive documents with negative ones" or "Combine positive and negative documents automatically" under Combine Flag. 
If the configuration is right, then open app "Create Outbound Files" and select the negative billing document and you can see its Material.
Finally, choose a positive billing document which contained the same Material and the amount is not smaller than the negative billing document and combine them.
After the negative billing document combined, other positive billing documents can combined successfully.

create outbound files, negative billing document, combine , KBA , FI-LOC-GTI-CN , China , Problem