Hey @Fran55 .
Thanks for the quick response.
In this case, if you are still experiencing the same issue with purchasing a paid theme from the Shopify Theme Store, we may need to take a further look into your online store setup. Since I cannot authenticate you over the Community Forums due to the sensitive information that needs to be shared, I am unable to view the specifics.
You can get in touch with our live support by logging into your online store using the Contact Us page. This will allow us to securely verify you as the store owner.
Once you successfully login - you will be directed to the Help Center. Select the topic that you would like assistance with to locate the options to Get Support and speak directly with a Support Advisor about purchasing a paid theme.
Let me know if you have any questions.