On a bare-metal platform, wc_InitRng() needs a valid entropy source. If your MCU has a hardware TRNG, you'll need to configure wolfSSL to use it instead of the default RNG. Make sure the TRNG is initialized first and, if your platform isn't already supported, implement a custom hardware RNG interface. Also, sharing your MCU, wolfSSL version, and the exact error code would help narrow down the issue.