Hi @Ric_Orna,
I agree it’s not spelled out as clear as it could be in the API docs but most of the info is there. See for example Custom fields
For enum and number, just follow the syntax shown there (for enum, but sure to supply the enum option’s gid, not the text name of the option).
For multi-enum and people, it’s an array since you can have multiple values: Add custom field value - #2 by Phil_Seeman
For multi_enum, the values to be supplied are multi_enum option gids. For people they’re user gids.
And for reference, the complete schema for the custom field object: https://developers.asana.com/reference/custom-fields#customfield