QuicKbooks error

I am getting :
Error QBWC1048: QuickBooks Web Connector Could not verify the web application server certificate. Error QBWC1051: The new application was not added
in Quickbook web connector while importing qwc file.
I have created Web Service in Salesforce and using Salesforce as SOAP Server. Then, using the Salesforce public URL in AppURL of qwc file.
I have also tried after disabling the SSL security(SSL 2.0 and SSL 3.0)and firewall but getting the same problem.
While checking on SOAP UI tool, getting the required data.
I've been advised to use QuickBooks 2020 or install QuickBooks on DaaS Windows
Please help where I am doing wrong.
Many thanks in advance.