In order to use the screen values for a field in the data source, you have to add it as dependent field.
Example: Let's suppose we have two custom fields: one KCF - Single Autocomplete and one KCF - Multiple Autocomplete, the second one is populated depending on the value of the first one.
An easy example would be: the first custom field has five option, representing the five continents , and the second one contains the countries from some table ("countries"), depending on the value selected on the first one.
You can see the corresponding data sources below:
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In the issue view screen, the result would look like this:
