How to Reprocess M Message in Customs Declaration Document in SAP GTS
Situation:-
The export declaration “M” message for the Customs declaration document has already been processed successfully in SAP GTS but we are not getting any update from the Customs authority due to some technical glitch.
Requirement:-
The business user wants to reprocess the “M” message in the customs declaration document in SAP GTS again to send data to the customs authority.
Issue:-
User can not retrigger this “M” message again because the customs declaration document has been frozen until unless receiving any “I” message against the respective customs declaration document from the customs authority. 
As you can see the user is unable to open this customs declaration document in change mode because it is already processed which means the SAP GTS Clearance Document can not process due to its status.
Solution:-
Step1:- Current status of the Clearance document through change log. 
Step2:- Reset the Processing status of the document
T.code:- /n/SAPSLL/CDOC_STARES
Provide applicable FTO code, Customs Declaration document number, and year then click on execute button. 
Click on the “Reset Status” button which will change the status of that document so that the document can be opened in change or edit mode. 
Now processing status of the SAP GTS Customs Clearance document has been changed from 2A to 1A.
Step2:- Repeat M message in Customs declaration document.
Now you can see the Customs clearance document has been opened in change mode, and in the communication, the tab selects the “M” message and click on the “Repeat Message” button.
Now the system has added the same M message again and disables the previous one, then we have to click the save button to generate IDOC to send export declaration information to the concerned customs authority.
On save system switched document status to DISPLAY mode again.
Now processing status changed to 2A due to this it will allow editing this document until unless receiving any “I” message.