Hello @muktupavels! Apologies for the late response. We appreciate you in exhausting our helpful sites and documentation regarding your concern. It was indeed mentioned here that the base min order size (API field name: base_min_size) together with base_max_size, max_market_funds from our market parameters was deprecated last June 30, 2022 but this is only for Coinbase Exchange/Pro only. The Advance Trade API still holds the “base_min_size” and if the value is too small, then the call will get rejected followed by the "PREVIEW_INVALID_BASE_SIZE_TOO_SMALL" error. It is still active for now but eventually, the base_min_size will be soon also deprecated under this product.
Appreciate your patience and understanding! Thank you!