In order to pay for a license, you need to OWN the company, not "share" the company. Review that you are indeed the OWNER of the company first before purchasing a license.
If your Budgeto account has more than 1 company, you will have to select a plan (with the options) for each and everyone of them.
To do so, access your company list and select the one you need to attribute a plan to.
Once in the company, press on the upgrade button on the top of the page.
This will bring you to the subscription page.
- Select if this company is billed annually on yearly (1).
- Add options to this budget (2).
- Press on upgrade and validate on the checkout page (3).