how to fix A technical problem with the server created an error. Try again to continue what you were doing?

i make mistake in index.php in root folder

i added some code that was not removed

this was just messing with the api calls from admin panel because it was corrupting json output.

for reference : https://tutes.in/solved-magento-2-error-a-technical-problem-with-the-server-created-an-error-try-again-to-continue-what-you-were-doing-if-the-problem-persists-try-again-later/

This error can occur when there is a problem applying a filter to the current grid. It can be cleared by removing the records from the ui_bookmark table for your user.

If you aren't sure about your user id, run SELECT email, user_id FROM admin_user;.

Then run DELETE FROM ui_bookmark WHERE user_id = [USER ID]

This should clear the stored filter. However, it won't fix the underlying problem, so if you use the same filter, the error will occur again.

In the case I was investigating, it turned out that the data migration tool had migrated a product with no SKU. Giving it a value for SKU prevented the filter error.