Pet urine starts out acidic which is easily removed with alkaline cleaners and spot removers.
But after pet urine dries it becomes alkaline itself and will not attract to normal stain removal products. Often it can be removed using an acidic product such as vinegar (white has less odor).
If you have dried urine spots and do not have pet urine stain removal handy, apply some white vinegar and allow a few minutes to dwell. Remove as much liquid as possible using dry towels. Press hard to absorb what is in pad. Do not rub, that can damage the carpet fibers. This should remove most of the stain.
When we clean your carpet next we can remove more of the stain and greatly reduce any lingering odors.
Accidents will happen!