GETPIVOTDATA() with a pivot table from a data model

I am trying to understand how to use GETPIVOTDATA() when it is used with a pivot table from a data model.

I have a table that looks like this;

Date Count of LTC
27/04/2021 17026
28/04/2021 24621
29/04/2021 23201
30/04/2021 12878

The date column comes from a data model table (DataModelTable) with a column called UPDATE_TIME. The Count of LTC column comes from the same table in the data model.

What I want to be able to do is have a cell elsewhere on my worksheet where a date can be entered, and use GETPIVOTDATA to retrieve the 'Count of LTC' value. I have used GETPIVOTDATA() to get the data I want by clicking on cells and get this formula.

=GETPIVOTDATA("[Measures].[Count of LTC]",$B$4,"[DataModelTable].[UPDATE_DATETIME]","[DataModelTable].[UPDATE_DATETIME].&[2021-04-27T00:00:00]")

The first cell in my Pivot Table is at cell B4. The above of course works. Using this as a template of the formula I need I have created this....

=GETPIVOTDATA("[Measures].[Count of LTC]",$B$4,"[DataModelTable].[UPDATE_DATETIME]",I25)

Cell I25 has a date in it (27/04/21). The result I get back is a '#REF!' error. The only difference as I see it is the way that I have expressed the date. The date in the Pivot Table (Data Model) is a full date timestamp. This makes me think that I need to expand my date in I25 to a full timestamp. If so, how can I do that?

Any guidance, suggestions or solutions will be very welcome.

TIA

assuming I25 holds a date (no time) then:

=GETPIVOTDATA("[Measures].[Count of LTC]",$B$4,"[DataModelTable].[UPDATE_DATETIME]","[DataModelTable].[UPDATE_DATETIME].&["&TEXT(I25,"YYYY-MM-DD")&"T00:00:00]")

Thanks for this. I was coming to this conclusion from other research I have done. What you have proposed works.