If you are trying to save a subscription product on Shopify and have checked the box 'Only show this product with these purchase options' but it's not saving, here's how to fix this.

The product is most likely in too many sales channels that are not eligible for subscription only products.

To solve this issue, you can remove or de-listed the ineligible sales channels

(such as Point of Sale & Shop) & Shopify will allow you to save the product as a Subscription only product without the one time purchase option.

If you are able to remove this product from POS and shop, that will resolve the issue of allowing you to save this as a subscription only product.

Issue: Are you seeing too many sales channels listed like this example below?

Solution: Remove the extra sales channels.

Shopify > Publishing > Manage Sales Channels > you should see only Online Store