Hi,
Create a custom module or use your existing one. Add the following controller in controllers/main.py:
from odoo import http
from odoo.http import request
from datetime import datetime
class ProductConfiguratorController(http.Controller):
    @http.route(
        route='/sale/product_configurator/update_combination',
        type='json',
        auth='user',
        methods=['POST'],
    )
    def sale_product_configurator_update_combination(
        self,
        product_template_id,
        ptav_ids,
        currency_id,
        so_date,
        quantity,
        product_uom_id=None,
        company_id=None,
        pricelist_id=None,
        **kwargs,
    ):
        if company_id:
            request.update_context(allowed_company_ids=[company_id])
        product_template = request.env['product.template'].browse(product_template_id)
        combination = request.env['product.template.attribute.value'].browse(ptav_ids)
        product = product_template._get_variant_for_combination(combination)
        pricelist = request.env['product.pricelist'].browse(pricelist_id)
        product_uom = request.env['uom.uom'].browse(product_uom_id)
        currency = request.env['res.currency'].browse(currency_id)
        # Use _get_basic_product_information to fetch all necessary info
        values = self._get_basic_product_information(
            product,
            pricelist,
            combination,
            quantity=quantity or 0.0,
            uom=product_uom,
            currency=currency,
            date=datetime.fromisoformat(so_date),
            **kwargs,
        )
        # ⛔ Remove computed price — set variant's list price (sales price)
        values['price'] = product.lst_price
        return values
def _get_basic_product_information(
    self,
    product,
    pricelist,
    combination,
    quantity,
    uom,
    currency,
    date,
    **kwargs,
):
    name = product.get_product_multiline_description_sale()
    return {
        'product_id': product.id,
        'product_template_id': product.product_tmpl_id.id,
        'combination': combination.ids,
        'name': name,
        'price': pricelist.get_product_price(product, quantity, request.env.user.partner_id),
        'product_uom': uom.id if uom else product.uom_id.id,
        'currency_id': currency.id,
    }
Hope it helps
Did you change _compute_product_lst_price()? Because ultimately: product.lst_price = list_price + product.price_extra