Making such moves puts you at risk of being booted from the platform site(s) you use. I’m not joking. Even mentioning at NiteFlirt, for example, other platform sites you use can get you banned for going against Terms Of Service (TOS). So even if your client, however softly, threatens that you’ll lose them if you don’t accommodate their request, you have to ask yourself if being blacklisted at the platform you work at is worth the discussion.
Aside from this practicality, there are other issues.
Even if the offer comes to you via another source, say direct email, contact off your website, Twitter, etc., there’s just no reason to take payments for services outside the phone sex platform site. (This includes clips sites, cam sites, etc.)
One of the number one “requested payment option” sites