Web App - mailto link not working??

I have looked for this answer everywhere! Most of the post are over 8years old and everything they state does not work.

I am testing my site on my iPhone using TestFlight so not sure if that is the reason or not?

I have a HTML website that is using a iframe to run as an APP

The issue I am having is when I press the email link noting happens ie the mail system on the iPhone does not load

I am not sure if this is because I am using test flight or not.

If I test my site on a standard web browser then the link works.

<a href='#' onclick='this.href=mailto:test@test.co.uk'>Link text</a>
<a href='mailto:test@test.co.uk'>Link text</a>


Hope you can find a solution as I really need this to work please


Thanks

Tim