Error in sharing a premium theme preview with others on a development store

[ProCommerce]

Hi there,

When I share the preview link with my client, it asks for the password two times, and when we enter the password 2nd, first it opens up the default published theme "Dawn", instead of the unpublished theme we are working on, and then by pasting the URL again, it opens the preview link.

It is a premium theme that we haven't bought yet but this shouldn't be the issue when we are sharing only a preview link.

Preview Link: (Valid for 2 days)
https://xo7qm4eb32188ix0-89668583729.shopifypreview.com
Password: lithee

Also, please confirm whether shopify allows you to buy a premium theme while the store is in development via our shopify partners account. Earlier, it wasn't allowed to connect a credit card in a development store and pay for any shopify app. Is it the same case if we have to buy a premium theme for a development store or what?