InviteMember supports two types of free trials:
with credit/debit card upfront;
without credit/debit card upfront.
Setting a trial period
To set a trial period, open your plan settings and click Edit trial period:

With credit/debit card upfront
By default, a trial period can only start with a credit/debit card upfront.
Please note that it will only work if two conditions are met:
the plan is recurring ("Recurring: ON" in plan settings);
the payment provider supports recurring subscriptions (Stripe/PayPal/Skrill/etc).
Otherwise, a free trial won't be offered.
For other payment methods (like CoinPayments, for example), please use the second mode described below.
Without credit/debit card upfront
To make the free trial available without credit card upfront, click Trial without card: OFF to set it to ON:

That's it!
Here is how your membership bot payment options look like now:

Note the Free Trial: 14 days button. When a user clicks it, the bot asks for a confirmation (trial periods can only be used once):

The trial is started after a confirmation.

When the trial period is over, the user will have to start a real plan.
Otherwise, he will be kicked from the plan resources.
Remove trial period
To remove trial period from a plan, click Edit trial period and type 0.