How to query by a new form field

IF you created the field correctly, then the data will be stored as postmeta in the transactions. So you’re going to want to do WP_Query of our give_payment Post type, then within that query do a Meta Query and sort by that. It’s a pretty complex query, but here’s a few resources to get you on your way:

A very good tutorial on WP_Query and querying postmeta:
https://code.tutsplus.com/articles/mastering-wordpress-meta-data-querying-posts-and-users-by-meta-data–wp-34606

Some example code we created to help users like you to see how you can query the give_payment post type:
https://github.com/WordImpress/Give-Snippet-Library/blob/master/queries/sample-transaction-queries.php

Good luck!