Relate Many to Many in For All

[AnthonyDo]

Hi,

I am trying to relate an extra cost to multiple trainees. You can see the Many-to-many relationship in the picture below.

I have a form 'frmAddExtraCostAddTraining'.

I have a collection 'colSelectedTraineesAddTraining' which holds all the trainees i want to relate to.

I have a button on select: 

ForAll(
    colSelectedTraineesAddTraining,
    Relate(
        frmAddExtraCostAddTraining.LastSubmit.cref8_ExtraCost_cref8_Trainee_cref8_Train,
        ThisRecord
    )
);

I have a gallery which has all the trainees in it. It has a label in the gallery with the following code:

Text(
    varTrainingPrice + Sum(
            ThisItem.'Extra Costs'
        ,
        If(
            cref8_vatinvoice = 'VAT Invoice (Extra Costs)'.'1',
            cref8_pricevatexcluded,
            cref8_price
        )
    ),
    "###,###,##0.00"
)

When i add an extra cost the gallery label 'cost' doesn't change so i don't think the relate function works. Anyone knows how to do this?

Greetings,

Anthony