Cannot convert account with Medium Plan to Organization

I have an account with medium plan and I want to convert it to an organization.

I have followed the steps in the documentation and created another account (community user) to assign as the owner for the organization.

When I click Convert and Purchase I get the following error:

Something went wrong. We can not convert your account at this time.

Is there something I’m missing and not included in the documentation? should the other account have a different plan or something (pro or medium)?