This happens when the theme or another plugin is using the gform_currencies filter and the currency array it is returning is missing the “code” property.
See the following example showing a currency properties array containing the “code” property: https://docs.gravityforms.com/gform_currencies/#h-2-add-indian-rupee
If you aren’t sure which theme or plugin is using the filter, you might need to run through a conflict test: https://docs.gravityforms.com/testing-for-a-themeplugin-conflict/