BC 17 - cannot enter table ID in field mapping from a data exchange definition

KSJ

Hi. I think this is something simple that I have missed but I am banging my head against a wall!
I am setting up a simple payment export. I have created the new data exchange definition, set the details (variable text and all code units etc), entered the line, entered the columns and then I go to field mapping and I try to enter the table id but I cannot. There is nothing showing in the drop down.
Any ideas? I am sure I must have missed a step but after reading and re-reading the documents I cannot find it at all! Any help will be greatly appreciated.

kriki

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