Hank here from Shopify.
The most common reason that your SSL is still pending is due to what is known as domain propagation which can take up to 72 hours to update across servers worldwide, although it is normally resolved within a few hours. However, when it goes outside of this, it is usually down to the DNS settings when connecting your domain.
The most important thing to note is to ensure that there are not multiple A records associated. You will need to ensure that only one A record is associated as this will have a direct effect with your SSL certificate. I will share a snippet from the guide below for ease of access!
Can you share your URL, and I can check the DNS settings? Note that once you make any changes to the URL, it can take up to 72 hours as previously mentioned.
Let me know if you have any further questions!