Do you mind clarifying what isn't working? It looks like for the first case you're using a HubSpot form and it works and on the second case you're using a WordPress form and it's not working? By not working do you mean that the submission isn't coming into HubSpot?
When looking to use non-HubSpot forms you may want to take a look at this documentation: Use non-HubSpot forms where it detailed down what are the supported forms in order for form submissions to be collected in HubSpot
Based on the documentation, it looks like we do support Native WordPress comment forms. Have you give that a try yet?
First, I created (on wordpress) a form using HubSpot plugin. It works great. Except there is a huge "branding line" under the form. I understand but I can't aford the paid version of hubspot ( for now ). So I have to use an other form.
So, I tried to install ninja form (on wordpress), last version. It didn't work. So I downgraded the plugin, and went to a version UNDER v3 (as said in the "non hubspot docs). Except neither the first solution, neither the other one seem to works.
So I installed an other plugin. Same results. And now I installed contact form 7, same results. Nothing is working.
If I fill a form and send a submission, nothing is added into Hubspot.
If you have review the and ensure that the forms is supported but the form submission is still not coming in HubSpot, it could be that there may be another WordPress plugin installed that conflicts with the HubSpot-WordPress plugin. In this case, you can either disable the plugin or review the following frequently asked questions for additional troubleshooting steps.
Additionally, do you mind sharing with me the WordPress page that has the non-working form on it?