What to do if I pay child support to my ex but when she applied she wasn’t working but now she has a job?

Your ex should have reported her income and her boyfriend's income on the income and expense declaration.

Changed circumstances (change in income) are grounds for you to seek a modification of child support.  File an Order to Show Cause (court form) requesting a modification of child support along with your supporting declarationd which states the facts in support of your request for a modification of child support.  File these documents with the court and a proof of service and serve a copy on your ex by mail.   You can use a court form proof of service or you can write your own.  If you write your own, it just says that you are at least eighteen years of age and the attached documents were sent via first class mail unless stated otherwise to ___________ (name and address of your ex) on __________ (date).  You sign and date at the bottom.  The date you sign should be the same as the date of mailing your documents and the same date you file your documents with the court.

When you file an Order to Show Cause with the court, the court will schedule a hearing on your request for a modification of child support.

Prior to filing your documents with the court, it would be advisable to check with the court clerk to be certain you are filing all of the appropriate documents for your request for a modification of child support because the required documents may vary from state to state.