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Not from the REDI API/DDE, but you may want to explore another Refinitiv API (e.g. Eikon) to see if it's supported there.
REDILIB Unsubscribe from market data for a given symbol
REDIPlus Send Order Failed : duplicated order and one more question is do the order sending via REDIPlus have limitation
REDI C# API
REDILIB resubscribe using same QuoteCache
REDI CacheControl Cell Names List