Why does my DATE_FORMAT give an error?

[Kim_Trager1]

I'm having a rollup field which is giving me the latest logged date from another linked table. The rollupfield is used in formular fields where it needs to show the date inserted into some text, but no matter what I do it gives me an error when I use the DATE_FORMAT() with the rollup field. 

I have the following very basic script in my test field:

DATETIME_FORMAT({Confirmed Delivery Date},'DD/MM/YYYY')

And i tried to add an ARRAYJOIN(), however nothing seem to work.

DATETIME_FORMAT(ARRAYJOIN({Confirmed Delivery Date}),'DD/MM/YYYY')

 Does anyone know where this can be going wrong?

[Kim_Trager1]

Figured out myself the rolled up date was not an actual date but a string so had to parse it first