The custom data field is not showing on my Stripe Payment Integration.

I see the problem you described on your form. When I checked the Stripe payment field, there is no Custom Data field available.

As described on the user guide, the Stripe field Custom Data field will only becomes available if you have a Textbox (Short Entry field) in your form that can be used for the custom data field.

Ex:

I suggest you try first adding a Textbox field on your form and run the Stripe field configuration again to check if Custom Data field becomes available.

Let us know if this did not work.