We do have limits in place when sending one time text campaigns in Retention Pro to protect your number from being marked as spam by the mobile carriers.
You can only send 1 “blast” style (or one time) text campaign to a maximum of 300 customers at a time, every 48 hours. This measure is in place to protect the phone number that is used to send out your campaigns.
Without these limits in place, if your number was marked as Spam by the carriers, you would need to be assigned a new number. That new number would then have to be registered to be 10DLC Compliant before you could send out any text messages.
If you are attempting to send a campaign that exceeds the limits you will see these error messages on the left side of the campaign edit screen and you will not be able to click Finalize and Send.
For more on one time campaigns please see: