Buying shares at fair value if certain conditions are met

[Leo]

Company A and company B hold Company C (60% by A and 40% by B).

What would be the accounting entries in company A, if company A has entered into an agreement with company B over the shares of C, if PBT of C reaches a certain level, then Company A is obliged to by 5% of company C at fair value at the time of the event?

I'm thinking of:
Dr: Investment
Cr: Liability (as per IAS 32 with subsequent changes in fair value in P&L)

I'm not sure whether debiting investment is correct.

Any thoughts?

[Leo]

Or
Dr other equity
Cr liability

I think this makes more sense

[Leo]

Or eventually,

Dr financial asset (for it will receive the shares in company C)
Dr liability

Eventually, the financial asset is fair valued, same as the financial liability, therefore, the effect of the financial assets cancel the liability so no P&L changes until the shares actually bought out?