Hi there Duckdivin,
We'll need more information to see how we can help. What slide button are you referring to exactly? Are you referring to using the side button on your iPhone to make purchases with Apple Pay? If so, make sure you're following these steps: Make purchases using Apple Pay - Apple Support
If that doesn't help, let us know which iPhone you have and the iOS version listed in Settings > General > About > Software Version.
If the side button doesn't seem to be working at all, work through these suggestions, including contacting Apple to set up service for your device:
If a button or switch isn't working on your iPhone or iPad, here are a few steps that might fix the issue. If they don't, you'll need to set up a repair.
1. Remove any protective films or cases that might block the button or switch.
2. Check for debris or dirt around the button or switch and clean with a soft cloth.
3. If the button or switch still isn't working, is damaged, or works intermittently, you can set up a repair:

Set up an iPhone repair
You'll find this information here: If a button or switch isn't working on your iPhone or iPad
Take care.