Same booking id

Hello.
By default the ID of booking can not be = 0, at all.
Its unique auto increment field in the Database, that have to start from 1 and increment with each new booking at 1.
If you see at the Booking Listing page at the left side the ID of bookings as 0, so then something wrong with configuration at your Database.

Please try to make FULL reinstall of the Booking Calendar plugin (its mean that booking data will be erased).

For this please open the general booking settings page and make checked the “Delete booking data during deactivation of plugin” at the right side.
then open the WordPress plugins menu and click on “Deactivate” link. Wait for the message that plugin is deactivated successfully.

After this Click on “Activate” link of Booking Calendar plugin and wait for the message that plugin is activated successfully.

Otherwise if you still will have this issue, please recheck with phpMyAdmin or other DB tool that the field booking_id have AUTO_INCREMENT status and was set as Primary Key. If you do not see this, so then something make restrictions to activate this options during activation of plugin. Please contact support of your hosting, so let thee recheck that your MYSQL user, have the rights for creation of new tables in your DB, and altering tables. For ability to set some fields as primary key with AUTO_INCREMENT status