fix: improve invalid channel error message returned

[kangmingtay]

What kind of change does this PR introduce?

• Improve error message around invalid channel error for phone auth. Only twilio and twilio verify support whatsapp as a valid channel.

[coveralls]

Pull Request Test Coverage Report for Build 12755234219

Warning: This coverage report may be inaccurate.

This pull request's base commit is no longer the HEAD commit of its target branch. This means it includes changes from outside the original pull request, including, potentially, unrelated coverage changes.

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Details

• 0 of 0 changed or added relevant lines in 0 files are covered.
• No unchanged relevant lines lost coverage.
• Overall coverage remained the same at 65.435%

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Totals
Change from base Build 12707782762:	0.0%
Covered Lines:	9814
Relevant Lines:	14998

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💛 - Coveralls