Why has our store's conversion rate gone down?

It's tough to say what affected the conversion rate because you changed multiple things at the same time and didn't run Split Tests. You switched themes, altered the design, and started running new campaigns that send new traffic. Now, you can't tell what effect each of the changes had because they were not done separately. You're not alone with that; it is a common mistake. There is a straightforward methodology to Conversion Rate Optimization that you should follow. Every change that you make is like a new version, and every new version has to be tested against the older version to see which one is better. The versions have to be tested simultaneously to avoid any outside factors from affecting your results. It is like a tournament, where the best version wins and advances to the next step. The problem is that people often don't follow this methodology and make multiple changes at once without testing their effect. And then they lose twice: 1. They don't know which change had a positive impact, which had a negative impact, and to what extent each change affected their conversion rate. 2. They miss a critical opportunity to learn about their customers. If they measured the effects of their change, they would understand their customers' behavior better. Another thing is that a new and better design doesn't necessarily mean better conversion rates. Especially not if the old design was changed again and again to improve conversions. It's like trying to improve the evolution of a product with a single attempt. Chances are that you're going to miss. Therefore, it's best to make changes gradually, test, and learn from them. As I see it since you have already made multiple changes, now you have three options: 1. Compare the performance of the new design with the old one. In order to really know how your changes affected conversion rates, you need to compare the new version of your Shopify store with the old one. This option may be a bit complicated for some merchants, and you might need to hire a developer to help you. Run both versions of the store at the same time with the same traffic in an AB Test to determine which version has a better conversion rate. If you do that, you'll know for sure which version works better. If you can't compare the entire new version with the old one, then you should consider the second option. 2. Revert all changes and start over. This is the safe option, even though it isn't popular because people don't like to cancel the work and time they have invested. But if you select this option, you'll have a scientific way to know how each change affects your conversion rate. Reset all changes - Go back to the old theme with the old design, and stop the ad campaigns. Now, start redoing the changes again. But now, make just one change at a time and run a Split Test against the old version. Once you decide which version converts best, keep it and move on to test the next change. Now you're following a scientific methodology to optimize conversion rates. Stick to it and see how it improves over time. If you don't want to cancel all your changes and start over, then go for the third option. 3. Improve the new version of your store. If you have made a lot of changes that would be too expensive to undo, you can simply look at the performance of the current version of your store as your baseline, and start optimizing it. Make sure you follow the Conversion Rate Optimization methodology.