Instrument details such as tick sizes is found in the GET /ref/v1/instruments/details/{Uic}/{AssetType} endpoint. The response either includes a single decimal tick size (look for the field TickSize) or a whole scheme of tick sizes depending on the current market price (look for the field TickSizeScheme). In case of OTC products the tick size is set by Saxo Bank and for ETPs they are set by the exchanges.
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