Pointer confusion

[gfvalvo]

@gcjr

presumably the arguments to esp_now_send() are an address, a pointer to sequence of bytes and the number of bytes to send.

Right.
Looking in esp_now.h, you'll find the function's prototype:

esp_err_t esp_now_send(const uint8_t *peer_addr, const uint8_t *data, size_t len);

Note that the type of the second parameter is 'const uint8_t *'

@iangill

or is this just to store the size in bytes of the data?

No, 'sizeof(myData)' the size in bytes of the data.