@ComputerHabit2
There is no need for all of the actions that you have going on.
All you need is to First:
Set the Items property of your Combobox to:
Ungroup(
Table({Items: 'New APPA List'.appaNumber},
{Items: 'Revision APPA List'.appaNumber},
{Items: 'Tranfer APPA List'.appaNumber}
),
"Items"
)
Then set the DefaultSelectedItems property of your combobox to:
RenameColumns(
Filter(Split(Parent.Default, ";"),
!IsBlank(Result)
),
"Result", "appaNumber"
)
(NOTE: The difference before is that you were never matching a record. You were using (by renaming the column from Result to Value) a Value column to match the Items...but the Items property has records with only an appaNumber. So the above corrects that)
Your Update property is correct (except you were referencing a non-existent column - which means you would have had nothing):
Concat(cmbRelatedAppa.SelectedItems, appaNumber, ";")
There is no need for the OnChange of the Combobox. In fact, you don't want to use the OnChange action on comboboxes as they will execute even when setting the default items selected.
That is it! It should give you what you need.