Unable to place order

[2base]

Magento Version 2.1.9
While placing an order got an error like this.

Exception.log:

Next Exception: Report ID: webapi-5c303b3cb8362; Message: Method does not exist in /home/125717.cloudwaysapps.com/zjwtcugvqe/public_html/vendor/magento/framework/Webapi/ErrorProcessor.php:195

debug.log:

[2019-01-05 05:06:04] main.DEBUG: SQL Results: {"0":{"pk":"11946","website_id":"1","dest_country_id":"SA","dest_region_id":"0","dest_city":"","dest_zip":"","dest_zip_to":"","condition_name":"package_weight","condition_from_value":"0.0000","condition_to_value":"5.0000","price":"30.0000","cost":"0.0000","shipping_method":"Aramex"},"1":{"pk":"11947","website_id":"1","dest_country_id":"SA","dest_region_id":"0","dest_city":"","dest_zip":"","dest_zip_to":"","condition_name":"package_weight","condition_from_value":"0.0000","condition_to_value":"15.0000","price":"24.0000","cost":"0.0000","shipping_method":"Dhl"},"is_exception":false} []

Payment is working fine if I disabled this module.
Site Url: https://www.mamatag.com
Screenshot of the checkout page: https://prnt.sc/m3b5pf

Thanks in advance