Facebook Conversion Pixle

[RFLIndustries]

Hello, I am wanting to do paid advertisement to try and get more people to my forum but only wanting to pay for those who join.

so you can do the conversion pixel but my question is how would you put it in?

the register.php handles both the registration as well as the thank you page.

if I was doing it I would put it on the Thank you page. but don't see how I can do that since they are both the same page

any help would be greatly appreciated