When you see an error message such as
E (61175) esp-tls-mbedtls: mbedtls_ssl_setup returned -0x7F00
on your microcontroller (e.g. ESP32), this means
MBEDTLS_ERR_SSL_ALLOC_FAILED
In other words, there is not enough memory for mbed-tls to work. Try to reduce the memory usage of your application.