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@NeilKY when you say within a formula do you mean inside the formula definition or within the results of the formula? It is possible to do this with the API but the approach is going to be a bit different depending on what you mean here. Let's assume you mean within the formula definition as that is more likely the case,

1. Get sheet (required via bridge, option via straight api)
2. Get all columns (can get direct from api, otherwise it is part of get sheet)
3. Iterate through all columns
4. for each column create a column update json object and put them into an array of json objects for update
5. process all column updates via the column update API, now all your formulas are done

you can use 1-5 to also rename anything in a column header or description if that is text you also want to change.

Now to do cells,
1. get sheet
2. get rows
3. interate through all rows
4. iterate through all columns
5. prepare JSON update object for each row (needs id, column id, and value)
6. process all row updates via the update row API

*deleted

ty for clarification @Marcela!

You can do this with the Update Column endpoint, if you first read the list of IDs from the first sheet, you can post those into the dropdown column on the second sheet as "options".

https://smartsheet.redoc.ly/tag/columns#operation/column-updateColumn

// Specify column properties
Column columnSpecification = new Column
{
  Id = 5005385858869124,
  Title = "First Column",
  Index = 0,
  Type = ColumnType.PICKLIST,
  Options = new string[] { "One", "Two"}
};

// Update column
Column updatedColumn = smartsheet.SheetResources.ColumnResources.UpdateColumn(
  2252168947361668,   // sheetId
  columnSpecification