Hreflang error from auditor - can you help me see the issue?

I have a shopify store setup with two regional domains, which using hreflang tags as populated by shopify. However when doing a website audit (Link Assistance Website Auditor) I get the error:

'It appears that some pages with hreflang elements either miss self-links or have no return-links from other language versions of a page. '

But I can't see the issue, and am wondering if anyone can help. Below is the example concerned from my head section (the second domain is just the account domain for shopify)

<link rel="alternate" hreflang="x-default" href="https://www.website.com.au/collections/shirts"><link rel="alternate" hreflang="en" href="https://website.myshopify.com/collections/shirts"><link rel="alternate" hreflang="en-NZ" href="https://www.erilan.co.nz/collections/shirts"><link rel="alternate" hreflang="en-AU" href="https://www.erilan.com.au/collections/shirts">