Hi R.E. van Wijk,
You can set the localization for a DateTime attribute in the entity so Mendix handles the DateTime as UTC time.
Also using the formatDateTimeUTC and parseDateTimeUTC, you can make sure that only UTC times are used.
I had a similar issue with date of birth for persons, and have solved it using UTC times.
More information about the DateTime can be found in the following article: https://docs.mendix.com/refguide7/datetime-handling-faq.
Hope this helps.
solution
Using the above steps results in request AND response using UTC