sites defaulting to main site url

My multisite install has defaulted to using the main site URL for sub domains instead of the sub domains url.

For example the main site is 123.com and I can visit this domain and the url remains 123.com

However if i visit abc.com which is a separate site on my multisite install when I select a page on the site the url changes from abc.com to 123.com/abc/?page_id=80 for example and not abc.com/?page_id=80

I have had a look at the permalink settings and can see that the 123.com url is used instead of abc.com

How do I get wp to display the correct url for the site accessed?

Thanks

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Resolved. I needed a domain mapping plugin