isEligibleForFreeTrial
Whether this user can currently start a free trial on this product.
Google Play filters the offer list per account: an account that has already used the trial for a subscription simply does not receive that offer in ProductDetails. So the presence of a trial offer is the eligibility signal, and this method is the honestly-named way to ask.
Use it to choose paywall copy — "Start 7-day free trial" versus "Subscribe" — instead of showing a trial the user cannot claim and having Play charge them immediately.
Only meaningful once product details have loaded; see isProductDetailsLoaded.
Return
true when a free-trial offer is available to this account.
Since
4.4.0
Parameters
productId
Subscription product id.