It seems that the FileBytes is in Base64 format. I am able to import an instrument list which contains "RIC,SAREUR=R" string in the imported file. Below is the message.

Post: https://hosted.datascopeapi.reuters.com/RestApi/v1/Extractions/InstrumentListImportFromBytes

{"FileBytes":"UklDLFNBUkVVUj1S", "Settings": {"ImportCreatedUserInstrumentsIntoList":true, "PredefinedAction":"Add", "AllowDuplicateInstruments":true, "PredefinedName":"test1", "ImportUserInstruments":true}, "FileName":"test1.csv" }

FileBytes must be in Base64 format.

If it is not (like XXX===) you will get the following error:

System.FormatException: The input is not a valid Base-64 string as it contains a non-base 64 character, more than two padding characters, or an illegal character among the padding characters.

Resolved. Thank You for the answers.

Using Veerapath's working request I was able to find that the issue elsewhere.

There's a typo in the API documentation:

/Extractions/InstrumentListsImportFromBytes vs

/Extractions/InstrumentListImportFromBytes

I should have read the response more carefully.

@filip.balas

Just a few additional thoughts:

Using this call you are storing an instrument list on the DSS server, permanently (well, until you decide to modify or delete it). This is mainly useful if you want to re-use the list later on. Storing an instrument list on the DSS server can be done in other ways, there are some examples in the tutorials here, in particular the REST API Tutorial 8 and the .Net SDK tutorial 2.

Depending on your use case, storing the list on the DSS server might not be required. Using On Demand queries you can pass the instrument list as a parameter, without storing it on the server. On Demand queries hide some of the complexity in the background, making you coding easier. To see examples of how that can be done, again refer to the tutorials here, in particular the REST API Tutorials 2 & 7, and the .Net SDK tutorials 6 & 7.

The best choice depends on what you are trying to achieve.