Eg. I have a dozen eggs to sell.

In this case, it can’t be written as ‘I’ve a dozen eggs to sell.’

But ‘have’ can be used as Modal Auxiliaries.

Eg:

They have solved many problems.

This can be written as

They’ve solved many problems’ using the abbreviated form of ‘have’.

But these days, we don’t follow this rule strictly & only Purists frown upon this usage.

That means, it is more or less accepted even in the case of using ‘ve’ for ‘have’ as the main, lexical Verb.

Abbreviating ‘have’ as ‘ve has become too widely accepted irrespective of whether the verb ‘have’ is lexical or modal auxiliary.

Hope this helps.