Plugin session and redirects

We have used the Salesforce plugin for our integrations. Now we need to get Google and Facebook referral codes from the URL such as ?gclid= and ?fbclid= to tell where we came to the salesforce form.

Problem here is that these come in internal redirects which means they redirect back to the form without referral codes which we need for the integration.

We have tried to make our own sessions but we get “PHP Warning: session_start(): Cannot start session when headers already sent in …”

We also tried with cookies but no luck. Is there a way to use sessions or cookies with this plugin. And if not, is there another way we can get the referral codes from the URL.