Biotherm’s checkout only has one promo box, and pasting a second code just overwrites the first. If you want to stack, wait for an automatic gift-with-purchase tier to trigger in your cart, then drop your discount code in. If that fails, honestly just grab it through Sephora during their sales.

They take cards and PayPal, but never pay full price. Biotherm runs 25% off sales all the time. Just watch the checkout screen; the promo box won't let you stack a discount with free gift offers. If you only need one bottle, buy through Sephora or Macy's to avoid their annoying shipping minimum.

Biotherm’s direct site is pretty stingy outside of Black Friday and their random Friends & Family sales. Honestly, if you need something now, sign up for their newsletter with a burner email to get the 15% code. Otherwise, just wait for a 25% sitewide event. They almost always throw in deluxe sample bags at checkout.

Biotherm’s direct returns are kind of a pain. You get 30 days from delivery, but there isn't an automated portal. You have to email their support with your order number to get an RMA authorized first. Honestly, if you're testing new stuff, just buy through Sephora to skip the mail-in hassle.