visualstudios's post in Should you ask for a review after the delivery? was marked as the answer
You can ask for a review upon delivery, you can't ask for a specific or positive review. This was confirmed by a Fiverr success manager and is current practice by multiple TRS and PRO sellers.
To give you an example, this exact wording has been confirmed to be totally fine to use on a delivery message:
"When you close the order, if you could go ahead and rate it and answer any Fiverr surveys, that would be really helpful for us!"