The "Error Validating Basket" message is tied to Olo's platform. This error is indicative of misconfigured menu items. Meaning the configuration in Olo's dashboard does not match what is in the POS.
Identify the location in question and the menu items being ordered (including any modifiers) and create a case with Olo by emailing firstname.lastname@example.org.
If more information is needed around basket testing, please see Olo's article titled Basket Testing.