Documentation
First-party delivery
The single biggest lever on accuracy, and the twenty lines of config it takes.
The problem
Safari's Intelligent Tracking Prevention erases script-writable storage (cookies and localStorage alike) after 7 days, and after 24 hours for a visitor who arrived on a cross-site ad click.
That 24 hour case is precisely your paid traffic. Served cross-origin, an iPhone buyer who returns on day two arrives as a stranger, and their purchase reports as unattributed.
The fix
The only storage ITP spares is a cookie set in an HTTP response from your own origin. So route the collector through a path on your own domain, and point data-api at it.
nginx
# Nginx
location /_rs/ {
proxy_pass https://api.roassensor.com/api/tracking/;
proxy_set_header Host api.roassensor.com;
proxy_set_header X-Forwarded-For $remote_addr;
}