無料 and 有料: a free first trial and paid later use
Compare a free trial with paid use, reading how 初回 and 以降 distinguish the first use from later uses and when charges apply.
No charge for the specified use
無料, read むりょう, means no charge for the specified use. 初回の体験は無料です。 says that the first trial session is free.
初回 identifies the first use. This sentence alone does not establish that the second and all later trials remain free.
Use that carries a charge
有料, read ゆうりょう, means that a charge applies. 二回目以降の利用は有料です。 says that using the service from the second time onward carries a charge.
有料で利用できます。 says that the service can be used for a fee. It establishes a charge but does not give the specific amount.
Contrasting counts and conditions
初回は無料、二回目以降は有料です。 gives different conditions for the first use and for use from the second time onward. 以降 includes its starting point, the second use, and those after it.
無料期間が終わったあとの料金を確認してください。 asks someone to check the charge after the free period ends. Separate later conditions from the current free-use notice.
Is the second use free in 初回は無料、二回目以降は有料です。?
Show the answer and why
No. 二回目以降 includes the second use, so it carries a charge under this notice.