Greetings, Adin7576.
I see that one of your Bluetooth accessories won't pair with your iPhone 8 Plus. That accessory will pair with your iPhone 6, however. Good job on the troubleshooting you've already accomplished and I'm happy to help.
If you can‘t connect a Bluetooth accessory to your iPhone, iPad, or iPod touch -- Follow the steps provided in this support article.
Take care!