The "Allow Existing Members to Subscribe to the Trial" option within each member plan is member plan specific. If you have the field marked NO within a particular member plan, this means that current (or previous) members who subscribe to that member plan will NOT receive/join that plan at the trial price/days, instead they immediately become part of the regular monthly plan that is set up.
If you have the field set to YES, then any members (current, expired, canceled) will be able to join that particular plan at the trial price, even if they were in another plan that did not allow members to subscribe to the trial.
There is another option available in the drop down menu: Yes, if Renewing From An Existing Plan. If it is necessary to always charge new members of this plan an intro or trial fee no matter their member status select this option. This means that if an existing member is currently on this plan and they have a billing failure (or otherwise need to renew), upon renewing they would only be charged the 'Plan Fee' as they had been prior to losing access to your site.
The setting will apply to any renewal no matter the users previous status
The field is "Allow Existing Members to Subscribe to the Trial?" and allows you to choose either YES or NO
Edit Member Plans
The Edit Member Plans page can be found under Members Edit Member Plans
Choose the member plan from the drop down menu
In the 'Allow Existing Members to Subscribe to the Trial' choose 'yes,' 'no,' or 'yes, if renewing from a different plan' from the drop down menu
Save the Changes
When all of the changes have been made, click on the found at the bottom of the page.
Understanding the Trial Fee Options
All members will incur the trial/intro fee everytime they subscribe/renew into this plan.
Any existing member will skip the trial/intro fee when they subscribe/renew into this plan. This includes any member account in the database regardless of existing plan or status.
Yes, if Renewing from a Different Plan
An existing member of other plans will incur the trial/intro fee when they subscribe or renew into this plan.
An existing member in this plan will incur the regular plan price when renewing into this plan.
This means that if a member of this plan has a billing failure, they would not have to pay the into/trial free again.