1) Code or snippet of the code. 2) Which version of esp32? 3) Which board ?
4) Description about your setup. Which device is acting like server and client.
In BLE the device hosts data ( can be a BLE enabled sensor) is called GATT server. The device which receives the device acts like GATT Client. This should not be confused with BLE Master and Slave. Slave can be GATT server. eg BLE enabled sensor.
BLE Characteristics can be set in the following modes
Read
Write
Notification
Indicate
In your project setup what is the client and server? BLE nodes can act like GATT server and client.
I would highly recommend you to go through the materials what Nordic Semiconductor has in their dev academy
