If you have an older Apple watch that just won’t charge anymore, Apple will fix it for free.
Apple says a system update caused the charging problem.
The new 7.31 update is available, which should prevent the problem from happening again.
A support site is available for customers with non-charging Series 5 and Apple Watch SE devices. If it doesn’t fix the problem, you can contact Apple support and set up a free, mail-in repair.