We recently had another user with a similar problem and their solution was to add the READ property to the TX characteristic in the UART service on their ESP32. Here’s their full message:
I programmed my ESP-32 as a server with one Service (UART service) and two characteristics RX and TX. On my RX was allowed only the property of WRITE and on my TX was allowed only the property of NOTIFY (this is done on one of the defaults examples on the ESP-32’s libraries). For some reason, this configuration works well with the iOS App but my ANDROID App couldn’t receive data from the SERVER. So, to make it work on ANDROID and iOS I added the following properties on my characteristics RX and TX: READ, WRITE, NOTIFY, INDICATE
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Actually, just adding the READ property on the TX characteristics of the the UART service is enough to solve this and make it work well.
Hope this helps.
-Mark