If the trip has already started, you will not be able to edit it. This will mean you can not click on and edit anything in the Trip Details section. There isn't a way to reverse this.
If you have an event that is happening over a long period of time, consider other options like a club or for the trip dates to be far in the future when the signup and payment deadline is if it isn't an actual trip to avoid not being able to make changes.
Before the trip start date, the Trip Details section is editable (you can see clickable small grey arrows).
After the trip start date, the Trip Details section will show no small grey arrows and is not editable. This is irreversible.
How can parents pay for a trip that has already started or happened?
As long as the student has been added to the trip (i.e. in the Confirmed tab under the Trip Participants section), they will still be able to make payments in the same way shown in this article.
What if parents didn't add their child to the trip?
Your school can manually add a child onto a trip and add a payment, even when the trip is currently running or has already happened using this article.