It's the caliper mounting bolts/bushing end that goes into the mounting arm (the metal part of the bolt/bushing) will not fit flush into the mounting arm

Where in this picture is it. Try and give me a number off the page. Click on the pdf file below. Top page is a 99 Camry 4 cylinder. Is this what you have?
28488

If you mean the "sliding pin" that goes into the rubber boot, that goes into the caliper bracket,.
If you can't twist it, or push it in and out, then it's seized. Those parts need replacing but I'll resort back to my original post to go get a reman caliper.